IMS: Grey out Wifi calling option when either sub is having call.

The WifiCallingSettingsForSub was not checking for call state reported
by telephony manager, hence, when call was on other sub, the option was not
getting greyed out.
Use the TelephonyManager API to fetch callstate.

Test: Manual

Bug: 130706399
Change-Id: Ib4b0e1191c83e23377ccf8ed013252728ef9dd95