UPSTREAM: Import cut down arc4ramdom.c from OpenBSD for better randomness.

Partially addresses #183.

(cherry picked from commit c140606bfb03da65fa5dab73b52b5c264748ddbd)

BUG=chromium:215026
TEST=(TODO: Use DHCP autotests)

Change-Id: I71e4db2ca13c07879382e0446d24d85bab3ad75b
Reviewed-on: https://gerrit.chromium.org/gerrit/31728
Commit-Queue: Paul Stewart <pstew@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
2 files changed