net: aquantia: Introduce rx refill threshold value

net: aquantia: Introduce rx refill threshold value

Before that, we've refilled ring even on single descriptor move.
Under high packet load that caused page allocation logic to be triggered
too often. That made overall ring processing slower.

Moreover, with page buffer reuse implemented, we should give a chance
higher networking levels to process received packets faster, release
the pages they consumed and therefore give a higher chance for these
pages to be reused.

RX ring is now refilled only when AQ_CFG_RX_REFILL_THRES or more
descriptors were processed (32 by default). Under regular traffic this
gives quite enough time for packet to be consumed and page to be reused.

Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>