If EVENT_NETWORK_INFO_CHANGED was handled after waitForIdle()
method done, this test will be failed due to
INetd#setTcpRWmemorySize() was not executed yet. Instead of
waiting for idle state, it's better to use NetworkCallback to
ensure events completely on ConnectivityService.
Bug: 140206578
Test: atest ConnectivityServiceTest#testTcpBufferReset\
--generate-new-metrics 500
Change-Id: Iad77415db38038603881d9ebe0e37586b549a45c
22e2195a8a