net/mlx5: Cleanup mlx5_ifc_fte_match_set_misc2_bits

Remove the "metadata_reg_b" field and all uses of this field in code
to match the device specification. As this field is not in use in SW
steering it is safe to remove it.

Signed-off-by: Raed Salem <raeds@mellanox.com>
Reviewed-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>