sfc: add functions to insert encap matches into the MAE

An encap match corresponds to an entry in the exact-match Outer Rule
 table; the lookup response includes the encap type (protocol) allowing
 the hardware to continue parsing into the inner headers.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>