bnx2x: properly update skb when mtu > 1500

bnx2x: properly update skb when mtu > 1500

Since commit e52fcb2462ac484e6dd6e68869536609f0216938 newly allocated
skb for small packets are not updated properly and dropped by stack.

(cherry picked from commit 036d2df9b3167598a9c9f1c13d9039f7e6cb0083)
Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Joe Jin <joe.jin@oracle.com>