Owing to a missing conditional, the result of rps_may_expire_flow() was
 being ignored and filters were being removed even if we'd decided not to
 expire them.

Fixes: f8d62037 ("sfc: ARFS filter IDs")
Signed-off-by: NEdward Cree <ecree@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>