mlxsw: pci: Set extra metadata in skb control block

Packets that are mirrored / sampled to the CPU have extra metadata
encoded in their corresponding Completion Queue Element (CQE). Retrieve
this metadata from the CQE and set it in the skb control block so that
it could be accessed by the switch driver (i.e., 'mlxsw_spectrum').

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>