Use new-style UID routing.

Kernel prebuilts for OC devices have been updated, so the legacy
attributes are not being used. Use the new attributes only. This
will ensure that devices aren't using the old code by mistake, as
any such devices will fail the VPN CTS tests.

(cherry picked from commit 882e467f)

Cherry-picking this to AOSP now that most external kernels have
been updated as well.

Bug: 16355602
Test: bullhead builds, boots
Test: netd_{unit,integration}_test pass
Test: has been running in internal master for several weeks.
Change-Id: I1c4e8c9281a843417a3a52294a1b7d3e6502bee6