net: busy-poll: return busypolling status to drivers

net: busy-poll: return busypolling status to drivers

NAPI drivers use napi_complete_done() or napi_complete() when
they drained RX ring and right before re-enabling device interrupts.

In busy polling, we can avoid interrupts being delivered since
we are polling RX ring in a controlled loop.

Drivers can chose to use napi_complete_done() return value
to reduce interrupts overhead while busy polling is active.

This is optional, legacy drivers should work fine even
if not updated.

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Cc: Adam Belay <[email protected]>
Cc: Tariq Toukan <[email protected]>
Cc: Yuval Mintz <[email protected]>
Cc: Ariel Elior <[email protected]>
Signed-off-by: David S. Miller <[email protected]>