mlxsw: spectrum: Report extra metadata to psample module

Make use of the previously added metadata and report it to the psample
module. The metadata is read from the skb's control block, which was
initialized by the bus driver (i.e., 'mlxsw_pci') after decoding the
packet's Completion Queue Element (CQE).

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