net/mlx5: Bridge, mark reg_c1 when pushing VLAN

On ingress VLAN push also assign value 0x7FE to reg_c1 tunnel id+opts
bits (tunnel id 0, which is not a valid tunnel id, and option 0x7FE which
was reserved by one of previous patches in the series). In following patch
the reg value is matched on egress miss to restore the packet to its
original state by removing the VLAN before passing it to the software data
path.

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Paul Blakey <paulb@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>