asix: fix infinite loop in rx_fixup()

asix: fix infinite loop in rx_fixup()

commit 6c15d74defd38e7e7f8805392578b7a1d508097e upstream.

At this point if skb->len happens to be 2, the subsequant skb_pull(skb, 4)
call won't work and the skb->len won't be decreased and won't ever reach 0,
resulting in an infinite loop.

With an ASIX 88772 under heavy load, without this patch, rx_fixup() reaches
an infinite loop in less than a minute. With this patch applied,
no infinite loop even after hours of heavy load.

Signed-off-by: Aurelien Jacobs <aurel@gnuage.org>
Cc: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>