[Telephony] Remove ACTION_MAIN for starting MobileNetworkActivity

Settings crashes because MobileNetworkActivity does not define the android.intent.action.MAIN in the AndroidMenifest intent-filter but CallFeaturesSetting does.

Bug: 224400995
Test:
1. Register to LTE-IMS.
2. Go to settings -> Network & Settings -> Disable VoLTE option.
3. Go to Dialer -> Settings -> and try to enable Video calling option.
4. Prompt will observed asking user to enable Enahnced 4G mode, click on that option.
5. Observe the behavior.
6. Crash will not happen.

Change-Id: I92dea477f3c815b447ffadf490da1b71a9b2eac8
1 file changed