RDMA/mlx5: Extend packet reformat verbs

We expose new actions:

L2_TO_L2_TUNNEL - A generic encap from L2 to L2, the data passed should
		  be the encapsulating headers.

L3_TUNNEL_TO_L2 - Will do decap where the inner packet starts from L3,
		  the data should be mac or mac + vlan (14 or 18 bytes).

L2_TO_L3_TUNNEL - Will do encap where is L2 of the original packet will
		  not be included, the data should be the encapsulating
		  header.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>