Update multiple validation result to ConnectivityService

Once a network is determined to have partial connectivity, it
cannot go back to full connectivity without a disconnect. This
is because NetworkMonitor can only communicate either
PARTIAL_CONNECTIVITY or VALID, but not both. Thus, multiple
validation results allow ConnectivityService to know the real
network status.

Bug: 129662877
Bug: 130683832
Test: atest FrameworksNetTests
Test: atest NetworkStackTests
Test: atest --generate-new-metrics 50
NetworkStackTests:com.android.server.connectivity.NetworkMonitorTest
Test: Simulate partial connectvitiy
Change-Id: I406c9368617c03a2dd3ab15fb1f6dbf539d7c714
Merged-In: I243db4c406cca826e803c8035268bc0c6e6e01e2
(cherry picked from commit 4532abd4)