This patch is to add redirect icmp packet process for ip6gre by
calling ip6_redirect() in ip6gre_err(), as in vti6_err.

Prior to this patch, there's even no route cache generated after
receiving redirect.
Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>