loginSip method
Implementation
@override
Future loginSip(String userName, String displayName, String password,
String sipIp, String port) async {
Map option = {};
option["username"] = userName;
option["password"] = password;
option["ip"] = sipIp;
option["port"] = port;
option["displayName"] = displayName;
return await methodChannel.invokeMethod('loginSip', option);
}