[monitoring-plugins] Show RTA as unknown if it can not be determined

[RincewindsHat]

 Module: monitoring-plugins
 Branch: master
 Commit: 0214ec1918abf589f15b70948ddba641a9729ce3
 Author: RincewindsHat <12514511+RincewindsHat at users.noreply.github.com>
   Date: Wed Nov 17 14:09:11 2021 +0100
    URL: https://www.monitoring-plugins.org/repositories/monitoring-plugins/commit/?id=0214ec1

Show RTA as unknown if it can not be determined

---

 plugins/check_ping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/plugins/check_ping.c b/plugins/check_ping.c
index 7d58b10..6aa43ed 100644
--- a/plugins/check_ping.c
+++ b/plugins/check_ping.c
@@ -171,7 +171,7 @@ main (int argc, char **argv)
 									  crta>0?TRUE:FALSE, crta,
 									  TRUE, 0, FALSE, 0));
 		} else {
-			printf("|");
+			printf("| rta=U;;;;;");
 		}
 		printf(" %s\n", perfdata ("pl", (long) pl, "%",
 		                          wpl>0?TRUE:FALSE, wpl,