Don't set the default firewall zone to wan if not specified to keep the
behavior aligned with other tunnel protocols like gre and 6rd.
If the interface zone is not specified try to get it from the firewall config
when constructing the procd firewall rule.
While at it only add procd inbound/outbound firewall rules if a zone is specified.
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>
f54611b06d