Add integration test to verify the incomplete IPv6 neighbors.

aosp/3013680 fixes the ignoring incomplete IPv6 neighbors logic, which
ingored the NUD failure event from unreachable IPv6 neighbor but didn't
guarantee the previous NUD probe result is null. Add integration test
to verify the behavior, i.e. only ignore the IPv6 neighbor which never
enters the reachable state, and we MUST NOT ignore the NUD failure if
the NUD probe result changes from probe to failed.

Bug: 335575053
Test: atest NetworkStackRootTests
Change-Id: I40463de9d165d66e282ae8286ca19f9974979539
1 file changed