net: skb_is_gso_v6() requires skb_is_gso()

bnx2x makes a dangerous use of skb_is_gso_v6().

It should first make sure skb is a gso packet

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Eilon Greenstein <eilong@broadcom.com>
Acked-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>