Add VTI Netlink Interface in NetD

Includes the logic to add / update / remove Virtual Tunnel Inteface
in RouteController.

Bug: 63589711
Test: Ran runtest -x "system/netd/tests/netd_integration_test.cpp"
Change-Id: I49a86f2eceecaf34fbb1e5dc05a888447437bef0
7 files changed