journald: make MaxFileSec really default to 1month

journald.conf(5) states that the default for MaxFileSec is one month,
but the code didn't respect that.

src/journal/journald-server.c

@@ -67,6 +67,7 @@
 #define DEFAULT_SYNC_INTERVAL_USEC (5*USEC_PER_MINUTE)
 #define DEFAULT_RATE_LIMIT_INTERVAL (30*USEC_PER_SEC)
 #define DEFAULT_RATE_LIMIT_BURST 1000
+#define DEFAULT_MAX_FILE_USEC USEC_PER_MONTH
 
 #define RECHECK_AVAILABLE_SPACE_USEC (30*USEC_PER_SEC)
 
@@ -1475,6 +1476,8 @@ int server_init(Server *s) {
         s->forward_to_syslog = true;
         s->forward_to_wall = true;
 
+        s->max_file_usec = DEFAULT_MAX_FILE_USEC;
+
         s->max_level_store = LOG_DEBUG;
         s->max_level_syslog = LOG_DEBUG;
         s->max_level_kmsg = LOG_NOTICE;