audio passthrough: fix forcing line in when trrs and line in are plugged in

Apparently I missed this at camp as I lacked a trrs cable (rather I was too lazy to go to my tent and fetch one but shh).

If you have both a trrs cable on line out and a cable on line-in, it defaults to trrs and does not let you force line-in mode.

This MR changes it so that line-in is preferred as a source, and lets all modes be forced as desired.

I've also verified that after this change everything works as intended (sans #70 (closed) but that's not a part of this) soo I shouldn't need to tweak this further very much.

python_payload/apps/audio_passthrough/__init__.py

@@ -108,10 +108,12 @@ class AudioPassthrough(Application):
         headset_connected = audio.headset_is_connected()
         if self._force_mode == "FORCE_MIC":
             audio.input_set_source(audio.INPUT_SOURCE_ONBOARD_MIC)
+        elif (
+            audio.line_in_is_connected() and self._force_mode == "AUTO"
+        ) or self._force_mode == "FORCE_LINE_IN":
+            audio.input_set_source(audio.INPUT_SOURCE_LINE_IN)
         elif headset_connected or self._force_mode == "FORCE_LINE_OUT":
             audio.input_set_source(audio.INPUT_SOURCE_HEADSET_MIC)
-        elif audio.line_in_is_connected() or self._force_mode == "FORCE_LINE_IN":
-            audio.input_set_source(audio.INPUT_SOURCE_LINE_IN)
         else:
             audio.input_set_source(audio.INPUT_SOURCE_NONE)