Read the peer deletion reason from the kernel

Read the peer deletion reason from the kernel

Recent FreeBSD kernels supply a reason for the OVPN_NOTIF_DEL_PEER
notification. Parse this from the nvlist so we can distinguish
user-requested removals from timeouts.

Signed-off-by: Kristof Provost <kprovost@netgate.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20221205164103.9190-4-kprovost@netgate.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25617.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 10ea19092ded38ff25a445f987ad948aa9eac49f)