openvpn: Update to version 2.5.6

openvpn: Update to version 2.5.6

- Update from version 2.5.4 to 2.5.6
- Update of rootfile not required
- No changes related to ciphers or options
- Source tarball changed from .xz to .gz as for version 2.5.6 the xz options was not
   available. Raised on Openvpn forum but response was that they also didn't know why xz
   option was not available but they thought it was not a big deal as the gz version is
   only slightly larger.
- Changelog
   Overview of changes in 2.5.6
	User-visible Changes
	    update copyright year to 2022
	New features
	    new plugin (sample-plugin/defer/multi-auth.c) to help testing with multiple
             parallel plugins that succeed/fail in direct/deferred mode
	    various build improvements (github actions etc)
	    upgrade pkcs11-helper to release 1.28.4
	Bugfixes
	    CVE-2022-0547 see
             https://community.openvpn.net/openvpn/wiki/SecurityAnnouncements
	      If openvpn is configured with multiple authentication plugins and more than
               one plugin tries to do deferred authentication, the result is not
               well-defined - creating a possible authentication bypass.
	      In this situation the server process will now abort itself with a clear log
               message. Only one plugin is allowed to do deferred authentication.
	    Fix "--mtu-disc maybe|yes" on Linux
	    Due to configure/syshead.h/#ifdef confusion, the code in question was not
             compiled-in since a long time. Fixed. Trac: #1452
	    Fix $common_name variable passed to scripts when username-as-common-name is
             in effect.
	      This was not consistently set - sometimes, OpenVPN exported the username,
               sometimes the common name from the client cert. Fixed. Trac: #1434
	    Fix potential memory leaks in add_route() and add_route_ipv6().
	    Apply connect-retry backoff only to one side of the connection in p2p mode.
             Without that fix/enhancement, two sides could end up only sending packets
              when the other end is not ready. Trac: #1010, #1384
	    remove unused sitnl.h file
	    clean up msvc build files, remove unused MSVC build .bat files
	    repair "--inactive" handling with a 'bytes' parameter larger than 2 Gbytes
	     due to integer overflow, this ended up being "0" on Linux, but on Windows
              with MSVC it ends up being "always 2 Gbyte", both not doing what is
              requested. Trac: #1448
	    repair handling of EC certificates on Windows with pkcs11-helper
	    (wrong compile-time defines for OpenSSL 1.1.1)
	Documentation
	    documentation improvements related to DynDNS. Trac: #1417
	    clean up documentation for --proto and related options
	    rebuild rst docs if input files change (proper dependency handling)
   Overview of changes in 2.5.5
	User-visible Changes
	    SWEET32/64bit cipher deprecation change was postponed to 2.7
	    Windows: use network address for emulated DHCP server as default this
             enables use of a /30 subnet, which is needed when connecting to OpenVPN Cloud.
	    require EC support in windows builds (this means it's no longer possible to
             build a Windows OpenVPN binary with an OpenSSL lib without EC support)
	New features
	    Windows build: use CFG and Spectre mitigations on MSVC builds
	    bring back OpenSSL config loading to Windows builds. OpenSSL config is
             loaded from %installdir%\ssl\openssl.cnf (typically:
             c:\program files\openvpn\ssl\openssl.cnf) if it exists.
	      This is important for some hardware tokens which need special OpenSSL
               config for correct operation. Trac #1296
	Bugfixes
	    Windows build: enable EKM
	    Windows build: improve various vcpkg related build issues
	    Windows build: fix regression related to non-writeable status files
             (Trac #1430)
	    Windows build: fix regression that broke OpenSSL EC support
	    Windows build: fix "product version" display (2.5..4 -> 2.5.4)
	    Windows build: fix regression preventing use of PKCS12 files
	    improve "make check" to notice if "openvpn --show-cipher" crashes
	    improve argv unit tests
	    ensure unit tests work with mbedTLS builds without BF-CBC ciphers
	    include "--push-remove" in the output of "openvpn --help"
	    fix error in iptables syntax in example firewall.sh script
	    fix "resolvconf -p" invocation in example "up" script
	    fix "common_name" environment for script calls when
             "--username-as-common-name" is in effect (Trac #1434)
	Documentation
	    move "push-peer-info" documentation from "server options" to "client"
             (where it belongs)
	    correct "foreign_option_{n}" typo in manpage
	    update IRC information in CONTRIBUTING.rst (libera.chat)
	    README.down-root: fix plugin module name

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Peter Müller <peter.mueller@ipfire.org>