fix: set GNU_SOURCE in mosquitto auth plugin

Author: dfranusic

src/services/sysagent/plugins/mosquitto_auth/plg_mosquitto_auth.c

@@ -8,6 +8,7 @@
  *
  */
 
+#include <umink_pkg_config.h>
 #include <string.h>
 #include <mosquitto_broker.h>
 #include <mosquitto.h>

src/services/sysagent/plugins/mosquitto_auth/plg_mosquitto_auth_v5.c

@@ -8,6 +8,7 @@
  *
  */
 
+#include <umink_pkg_config.h>
 #include <string.h>
 #include <mosquitto_broker.h>
 #include <mosquitto.h>