mlxsw: pci: Retrieve mirror reason from CQE during receive

In case the mirror reason is valid, retrieve it into the Rx information
so that it could be used during listener lookup in a later patch.

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