Add IPv6 address support for virtual ethernet pair

This is needed for testing DHCPv6.

BUG=chromium:496361
TEST=Upcoming client test network_Dhcpv6Basic

Change-Id: I977c06b8967e091aca4317f2c682caa1f95093b7
Reviewed-on: https://chromium-review.googlesource.com/281051
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Zeping Qiu <zqiu@chromium.org>
Tested-by: Zeping Qiu <zqiu@chromium.org>
1 file changed