net/mlx5e: Allow VLAN rewrite of prio field with the same match

Changing the prio field of the VLAN is not supported. With
commit 37410902874c ("net/mlx5e: Support VLAN modify action") zero
value indicated "no-change". Allow the vid rewrite if the prio match
is the same as the prio set value.

Fixes: 37410902874c ("net/mlx5e: Support VLAN modify action")
Signed-off-by: Eli Britstein <elibr@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>