Refactor extract_var_peer_info into standalone function and add ssl_util.c

Refactor extract_var_peer_info into standalone function and add ssl_util.c

Our "natural" place for this function would be ssl.c but ssl.c has a lot of
dependencies on all kinds of other compilation units so including ssl.c
into
unit tests is near impossible currently. Instead create a new file
ssl_util.c
that holds small utility functions like this one.

Patch v2: add newline add the end of sll_util.h and ssl_util.c

Patch v3: Refactor/clean up the function even more as suggested by Gert.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20210226111012.21269-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21585.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>