Reduce logspam about 'dco_update_keys: peer_id=-1' in p2p server mode

Reduce logspam about 'dco_update_keys: peer_id=-1' in p2p server mode

p2p --tls-server with no active client/peer logs once per second

  "dco_update_keys: peer_id=-1"

which does exactly nothing, except fill the disk.  So skip the call to
dco_update_keys() if peer_id == -1.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Antonio Quartulli <a@unstable.cc>
Message-Id: <20230109200011.2525342-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25935.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 85e0df6b493396d9d1d9030c4018f67037d2f12b)