net/mlx5: fix validation of VLAN PCP item

net/mlx5: fix validation of VLAN PCP item

Function mlx5_flow_validate_item_vlan() validates the user setting
is supported by NIC, using a mask with TCI mask 0x0fff.
This check will reject a flow rule specifying a vlan pcp item.

This patch updates mlx5_flow_validate_item_vlan() to use mask 0xffff,
so flow rules with vlan pcp item are accepted.

Fixes: 23c1d42c7138 ("net/mlx5: split flow validation to dedicated function")
Cc: stable@dpdk.org
Signed-off-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>