Revert "Revert "Block incoming non-VPN packets to apps under fully-routed VPN""

This reverts commit 3897df2e.

Reason for revert: Rolling forward, will fix tests in same CL stack.

Bug: 114231106
Bug: 130397860
Test: FrameworksNetTests
Change-Id: Ia8a0c99b4e1fd5dff26c881715cd876618ca4321