modules-load.c: allow MODULES_LOAD_PATH to be overridden

Define MODULES_LOAD_PATH only when it's unset, this allows it to be
overridden, for instance, by passing CFLAGS.

Signed-off-by: Ming Liu <liu.ming50@gmail.com>

plugins/modules-load.c

@@ -32,7 +32,9 @@
 #include "service.h"
 #include "conf.h"
 
+#ifndef MODULES_LOAD_PATH
 #define MODULES_LOAD_PATH "/etc/modules-load.d"
+#endif
 #define SERVICE_LINE \
 	":%d name:modprobe.%s [2345] /sbin/modprobe %s %s -- Kernel module: %s"