Add a command-line option to force the mDNS backend

Add this option to the system-v init script.

mdns.h

@@ -5,8 +5,10 @@ extern int mdns_pid;
 
 void mdns_unregister(void);
 void mdns_register(void);
+void mdns_ls_backends(void);
 
 typedef struct {
+    char *name;
     int (*mdns_register)(char *apname, int port);
     void (*mdns_unregister)(void);
 } mdns_backend;