Set o->use_peer_id flag for p2p mode

Set o->use_peer_id flag for p2p mode

There are two flags to indicate peer-id usage, one is
in tls_multi struct and another one is in options.

For P2P mode we don't set this flag in options,
which is used in MTU calculation. As a result,
automatically calculated MSS value in P2P mode is wrong,

Fix by bring use_peer_id flag in options and tls_multi
into sync for P2P.

Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Antonio Quartulli <a@unstable.cc>
Message-Id: <20220524091916.145-1-lstipakov@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24430.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>