sys_util: use checked arithmetic and alignment in sock_ctrl_msg
sys_util: use checked arithmetic and alignment in sock_ctrl_msg

Change-Id: I45125fc3a6af83e7f7ec791a2f9c5daef723ec89
Reviewed-on: https://chromium-review.googlesource.com/1277872
Commit-Ready: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>
Tested-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>
Reviewed-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm