{net, RDMA}/mlx5: Rename encap to reformat packet

Renames all encap mlx5_{core,ib} code to use the new naming of packet
reformat. This change doesn't introduce any function change and is
needed to properly reflect the operation being done by this action.
For example not only can we encapsulate a packet, but also decapsulate it.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>