ip6_tunnel: clean up ip4ip6 and ip6ip6's err_handlers

This patch is to remove some useless codes of redirect and fix some
indents on ip4ip6 and ip6ip6's err_handlers.

Note that redirect icmp packet is already processed in ip6_tnl_err,
the old redirect codes in ip4ip6_err actually never worked even
before this patch. Besides, there's no need to send redirect to
user's sk, it's for lower dst, so just remove it in this patch.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>