Restrict WiFi network connection

- Use StandardWifiEntry#canConnect() to determine if the network should
  be disabled or not.

- Use StandardWifiEntry#getSummary() to retrieve the restriction message.

- Disabled WiFi network if it cannot connect.

- If WiFi network is connected or saved network, leave it enabled to
disconnect or configure.

- See the result screenshot in b/203168943#comment11

Bug: 203168938
Bug: 203168943
Test: manual test
make RunSettingsRoboTests ROBOTEST_FILTER=LongPressWifiEntryPreferenceTest
make RunSettingsRoboTests ROBOTEST_FILTER=NetworkProviderSettingsTest

Merged-In: I04aafaa5b383598a0f87eea15d06b38bbc662b9e
Change-Id: I04aafaa5b383598a0f87eea15d06b38bbc662b9e
(cherry picked from commit f86bdc9c)