ipv4: warn once on passing AF_INET6 socket to ip_recv_error

One line change, in response to catching an occurrence of this bug.
See also fix f4713a3d

 ("net-timestamp: make tcp_recvmsg call ...")

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>