tun.c: undo_ifconfig_ipv4/6 remove useless gc argument

tun.c: undo_ifconfig_ipv4/6 remove useless gc argument

With the new networking APIs, each implementation handles garbage
collection internally and therefore does not require a gc object to be
provided by the outer layer.

However, there are a few cases where a garbage collector is still required.
In close_tun() move the declaration and cleanup of gc to the
area where it is used and simplify the surrounding code a bit.

While at it, fix a typo in a nearby ifdef comment.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20190805092529.9467-5-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg18726.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>