Fix flaky test for ConnectivityServiceTest#testPartialConnectivity

There are 2 problems will make testPartialConnectivity flaky:
1. If we call setNetworkValid() before expectCapabilitiesWith(),
there may be a timing issue that network will become VALID before
NetworkMonitor send PARTIAL_CONNECTIVITY to ConnectivityService.
Solution:
We should set network to valid after ConnectivityService received
NETWORK_TEST_RESULT_PARTIAL_CONNECTIVITY to ensure NetworkMonitor
will send PARTIAL_CONNECTIVITY to ConnectivityService first then
send VALID.

2. When test case call explicitlySelected(true) first then call
connect(true), NetworkMonitor will report the network validation
test result twice because ConnectivityServiceTest() will trigger
notifyNetworkTested() when setAcceptPartialConnectivity() is
called, it may cause a timing that before the second test result
send to ConnectivityService, connect() already called
setNetworkInvalid. So, NET_CAPABILITY_VALIDATED will be removed
and ConnectivityService will trigger onCapabilitiesChanged()
unexpectedly.
Solution:
Don't trigger notifyNetworkTested() when
setAcceptPartialConnectivity() is called. If there is needed,
use mCm.reportNetworkConnectivity() to report the test result
instead.

Bug: 128426024
Test: 1. atest FrameworksNetTests: \
      ConnectivityServiceTest#testPartialConnectivity \
      --generate-new-metrics 1000

Change-Id: I7200528378201a3c7c09a78ff827b41f2741dfa1