set the audio mode to voip

this seems to make two way audio happen on my s8

Author: danjenkins

android/src/main/java/io/wazo/callkeep/VoiceConnectionService.java

@@ -109,6 +109,7 @@ public void onAnswer() {
                 }
 
                 connection.setActive();
+                connection.setAudioModeIsVoip(true);
 
                 sendCallRequestToActivity(ACTION_ANSWER_CALL, null);
             }