relayctl: rename "empty" to "unavailable" in table status

The word empty suggested the table has no hosts configured. It really means
the table has no hosts currently up, so unavailable describes the state more
clearly.

OK?

Index: relayctl.c
===================================================================
RCS file: /cvs/src/usr.sbin/relayctl/relayctl.c,v
diff -u -p -r1.67 relayctl.c
--- relayctl.c	29 Aug 2026 09:36:49 -0000	1.67
+++ relayctl.c	29 Aug 2026 09:42:47 -0000
@@ -544,7 +544,7 @@ print_table_status(int up, int fl)
 	if (fl & F_DISABLE) {
 		snprintf(buf, sizeof(buf) - 1, "disabled");
 	} else if (!up) {
-		snprintf(buf, sizeof(buf) - 1, "empty");
+		snprintf(buf, sizeof(buf) - 1, "unavailable");
 	} else if (verbose)
 		snprintf(buf, sizeof(buf) - 1, "active (%d hosts)", up);
 	else