[mod_sofia] more fixes around md5 hash infoleak (tricky cfg).

[mod_sofia] more fixes around md5 hash infoleak (tricky cfg).

* [mod_sofia] md5 hash infoleak fixes: (explictly allow host set in gw params 'register_proxy' and 'outbound_proxy' to challenge too).

"We have tightened security for digest authentication on gateways.
If you have gateways configured using dns and not an ip address,
you may need to configure gw-auth-acl in gateway configuration to
specify the IP addresses you can send auth challenges to for this gateway.
This is meant to better secure who we will send auth challenges." (Mike Jerris)

[mod_sofia] add REGISTER/401 unit-tests (sipp based)

[mod_sofia] add INVITE/407 unit-test (sipp-based)

* Cleanup spacing

Co-authored-by: Andrey Volk <andywolk@gmail.com>