ipv6: Add an error handler for icmp6

ipv6: Add an error handler for icmp6

[ Upstream commit 6f809da27c94425e07be4a64d5093e1df95188e9 ]

pmtu and redirect events are now handled in the protocols error handler,
so add an error handler for icmp6 to do this. It is needed in the case
when we have no socket context. Based on a patch by Duan Jiong.

Reported-by: Duan Jiong <djduanjiong@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>