net: optimize napi_threaded_poll() vs RPS/RFS

We use napi_threaded_poll() in order to reduce our softirq dependency.

We can add a followup of 821eba96

 ("net: optimize napi_schedule_rps()")
to further remove the need of firing NET_RX_SOFTIRQ whenever
RPS/RFS are used.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>