bgmac: fix requests for extra polling calls from NAPI

After d75b1ade ("net: less interrupt masking in NAPI") polling
function has to return whole budget when it wants NAPI to call it again.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Cc: Felix Fietkau <nbd@openwrt.org>
Fixes: eb64e292 ("bgmac: leave interrupts disabled as long as there is work to do")
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>