netjack2: check config against MAX_CHANNELS

Check that the params don't include more than MAX_CHANNELS of audio or
else we overflow the position array.

Adapt to the compiled value of SPA_AUDIO_MAX_CHANNELS but allow at least
128 channels.

src/modules/module-netjack2/peer.c

@@ -9,6 +9,8 @@
 #endif
 
 #define MAX_CHANNELS	SPA_AUDIO_MAX_CHANNELS
+#define MAX_MIDI	128u
+#define MAX_PORTS	(MAX_CHANNELS > MAX_MIDI ? MAX_CHANNELS : MAX_MIDI)
 
 struct volume {
 	bool mute;