net_sched: act_vlan: Add priority option

The current vlan push action supports only vid and protocol options.
Add priority option.

Example script that adds vlan push action with vid and
priority:

tc filter add dev veth0 protocol ip parent ffff: \
	   flower \
	   	indev veth0 \
	   action vlan push id 100 priority 5

Signed-off-by: Hadar Hen Zion <hadarh@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>