sfc: add per-queue RX bytes stats

While this does add overhead to the fast path, it should be minimal
 as the cacheline should already be held for write from updating the
 queue's rx_packets stat.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>