clear unused slave netjack header fields.

As most NetJACK header fields are not set by the slave and thus may
contain anything (which looks weird on the wire), it makes sense to
actively clear the unused fields.

drivers/netjack/net_driver.c

@@ -233,6 +233,20 @@ net_driver_write (net_driver_t* driver, jack_nframes_t nframes)
     // offset packet_bufX by the packetheader.
     packet_bufX = packet_buf + sizeof(jacknet_packet_header) / sizeof(jack_default_audio_sample_t);
 
+		// clear unused header fields
+    pkthdr->capture_channels_audio = 0;
+    pkthdr->playback_channels_audio = 0;
+    pkthdr->capture_channels_midi = 0;
+    pkthdr->playback_channels_midi = 0;
+    pkthdr->period_size = 0;
+    pkthdr->sample_rate = 0;
+    pkthdr->transport_frame = 0;
+    pkthdr->transport_state = 0;
+    pkthdr->framecnt = 0;
+    pkthdr->reply_port = 0;
+    pkthdr->mtu = 0;
+
+		// set used header fields
     pkthdr->sync_state = sync_state;
     pkthdr->latency = netj->time_to_deadline;
     //printf( "time to deadline = %d  goodness=%d\n", (int)netj->time_to_deadline, netj->deadline_goodness );