sfc: add statistics for ARFS

Report the number of successful and failed insertions, and also the
 current count of filters, to aid in tuning e.g. rps_flow_cnt.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
3 files changed