Same reasoning as in bdedb798150a58ad7ce3c4741f2f31df97e84c3f; don't set
default firewall zone to wan as the firewall zone for the vti interface
can be configured in the firewall config or it makes it impossible not to
specify a firewall zone for the vti interface.
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>