Make --nobind default for --pull

Make --nobind default for --pull

Currently we default to local binding with udp. But the majority of
configuration files actually uses --nobind in the configuration to
change the default for --client. And client protocols should normally
use a random source port. This changes the default. Local binding with
--client can still be done using --bind.

This commit refactors the current code to be more easy to add to understand
and adds the the o->pull condition as additional option to opt into setting
local binding to false.

Patch v2: add more commments

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20211206010007.3072528-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg23303.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>