net/mlx5e: Allow dropping specific tunnel packets

In some case, we don't want to allow specific tunnel packets
to host that can avoid to take up high CPU (e.g network attacks).
But other tunnel packets which not matched in hardware will be
sent to host too.

    $ tc filter add dev vxlan_sys_4789 \
	    protocol ip chain 0 parent ffff: prio 1 handle 1 \
	    flower dst_ip 1.1.1.100 ip_proto tcp dst_port 80 \
	    enc_dst_ip 2.2.2.100 enc_key_id 100 enc_dst_port 4789 \
	    action tunnel_key unset pipe action drop

Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>