net/mlx5: Support MACsec over VLAN

MACsec device may have a VLAN device on top of it.
Detect MACsec state correctly under this condition,
and return the correct net device accordingly.

Signed-off-by: Emeel Hakim <ehakim@nvidia.com>
Reviewed-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>