sfc: handle non-zero chain_index on TC rules

Map it to an 8-bit recirc_id for use by the hardware.
Currently nothing in the driver is offloading 'goto chain' actions,
 so these rules cannot yet be hit.

Reviewed-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>