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: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>