ipv4: fix a bug in ping_err().

[ Upstream commit b531ed61 ]

We should get 'type' and 'code' from the outer ICMP header.

Signed-off-by: Li Wei <lw@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>