[Wi-Fi] Enhance com.android.settings.wifi.p2p unit test cases.

Add new unit test cases in WifiP2pSettingsTest.java, the coverage rate will raise from 30% to 71%.

Bug: 151696220
Test: make RunSettingsRoboTests ROBOTEST_FILTER=WifiP2pSettingsTest
Change-Id: I214866efae47a99e75178beca48deb398b70f9bd
2 files changed