sfc: populate enc_ip_tos matches in MAE outer rules

Currently tc.c will block them before they get here, but following
 patch will change that.
Use the extack message from efx_mae_check_encap_match_caps() instead
 of writing a new one, since there's now more being fed in than just
 an IP version.

Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>