Fix various 'Uninitialized scalar variable' warnings from Coverity

Fix various 'Uninitialized scalar variable' warnings from Coverity

These are all not actually problems, since the
uninitialized parts are either .unused members of the
struct (mroute_addr) or only written to (buflen), but
still doesn't hurt to explicitely initialize them.

Change-Id: I45cd0917d24570ae9e9db7eb6c370756e4595842
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Arne Schwabe <arne-openvpn@rfc2549.org>
Message-Id: <20231008103641.19864-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg27157.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>