ipv6: don't crash with corrupted control messages

Change-Id: I39f79ec43c73b2fcc90316713181940ada523150
Reviewed-on: https://go-review.googlesource.com/45114
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2 files changed