On Android different interfaces usually use different routing tables.
As a result, a change in interface should not be treated as route
update, but rather a remove and an add.
This change fixes a bug in VPN seamless handover where routes
failed to be updated when a new tunnel interface replaces the existing
one within the same network.
Bug: 158696878
Test: atest com.android.cts.net.HostsideVpnTests
Test: atest NetworkStackTests
Test: atest CtsNetTestCases
Test: atest FrameworksNetTests
Change-Id: I57987233d42a0253eaee2e1ca5f28728c2354620
bc4c5caa4f