monitor: Add set_link arguments completion.

Make it possible to query all net clients without specifying an ID when calling
qemu_find_net_clients_except().

This also adds the add_completion_option() function which is to be used for
other commands completions as well.

Signed-off-by: Hani Benhabiles <hani@linux.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/hmp.h b/hmp.h
index f8e16a8..91c9c85 100644
--- a/hmp.h
+++ b/hmp.h
@@ -100,5 +100,6 @@
 void sendkey_completion(ReadLineState *rs, int nb_args, const char *str);
 void chardev_remove_completion(ReadLineState *rs, int nb_args, const char *str);
 void chardev_add_completion(ReadLineState *rs, int nb_args, const char *str);
+void set_link_completion(ReadLineState *rs, int nb_args, const char *str);
 
 #endif