Hotfix for mavlink logbuffer, needs another round of validation.

src/modules/systemlib/mavlink_log.c

@@ -54,6 +54,14 @@ __EXPORT void mavlink_logbuffer_init(struct mavlink_logbuffer *lb, int size)
 	lb->elems = (struct mavlink_logmessage *)calloc(lb->size, sizeof(struct mavlink_logmessage));
 }
 
+__EXPORT void mavlink_logbuffer_destroy(struct mavlink_logbuffer *lb)
+{
+	lb->size  = 0;
+	lb->start = 0;
+	lb->count = 0;
+	free(lb->elems);
+}
+
 __EXPORT int mavlink_logbuffer_is_full(struct mavlink_logbuffer *lb)
 {
 	return lb->count == (int)lb->size;