ipv4: don't crash with corrupted control messages

Change-Id: I474b5832672e699f1eba1487f7f793bed3c1ff83
Reviewed-on: https://go-review.googlesource.com/45113
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2 files changed