net/mlx5e: Move tc tunnel parsing logic with the rest at tc_tun module

Currently, tunnel parsing is split between en_tc and tc_tun. The next
patch will replace the tunnel fields matching with a register match,
and will not need this parsing.

Move the tunnel parsing logic to tc_tun as a pre-step for skipping
it in the next patch.

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Oz Shlomo <ozsh@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>