ovpn: reset MAC header before passing skb up

ovpn: reset MAC header before passing skb up

After decapsulating a packet, the skb->mac_header still points to the
outer transport header.

Fix this by calling skb_reset_mac_header() in ovpn_netdev_write() to
ensure the MAC header points to the beginning of
the inner IP/network packet, as expected by the rest of the stack.

Reported-by: Minqiang Chen <ptpt52@gmail.com>
Fixes: 8534731dbf2d ("ovpn: implement packet processing")
Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>