devserver: work on system with kernel that does not support IPv6
devserver: work on system with kernel that does not support IPv6

BUG=none
TEST=Unittests. Verified that devserver now runs on non-IPv6 kernel.

Change-Id: Idc6a437bfc8c1f4dead169b5eda042c0cc82cf0a
Reviewed-on: https://gerrit.chromium.org/gerrit/39434
Reviewed-by: Chris Sosa <959d3d631fb6f17f1b07f751372041a1edb210d1@chromium.org>
Commit-Ready: Mandeep Singh Baines <19acf4ef1f391f4aab404dc5703cac3632e06f3a@chromium.org>
Tested-by: Mandeep Singh Baines <19acf4ef1f391f4aab404dc5703cac3632e06f3a@chromium.org>

coreos/dev-util,marineam/coreos-dev-util,mgireesh05/dev-util,mgireesh05/dev-util,coreos/dev-util,marineam/coreos-dev-util,mgireesh05/dev-util,coreos/dev-util