Add missing #include.

--- ax25-apps-0.0.8-rc5/ax25ipd/routing.c	2019-03-20 16:48:59.000000000 +0000
+++ ax25-apps-0.0.8-rc5/ax25ipd/routing.c	2025-07-05 02:59:28.748521455 +0100
@@ -8,6 +8,7 @@
 
 #include <memory.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <syslog.h>
 #include <arpa/inet.h>
 #include <netinet/in.h>