Implemented Idle timeout.

When set, a client that does not have any non-control traffic
for that period is getting disconnected.

src/worker.h

@@ -150,6 +150,9 @@ typedef struct worker_st {
 	/* for dead peer detection */
 	time_t last_msg_udp;
 	time_t last_msg_tcp;
+
+	time_t last_nc_msg; /* last message that wasn't control, on any channel */
+
 	time_t last_periodic_check;
 
 	/* set after authentication */