Do not use the length of the transmitted skb (which was freed), but
that of the response skb.

This issue was discovered using the Kernel Address sanitizer (KASan).
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Signed-off-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>