The instruction itself doesn't care what the bits it's twiddling represents,
even though the it was introduced to more efficiently manipulate IPv4 packets.

Change-Id: Ie65a6df4041ad2090060636ccf7128680fcf75b7
Reviewed-on: https://go-review.googlesource.com/21244Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>