journal: Add log level argument to journal_file_rotate_suggested()

When journald is rotating a file, we'd like to log the reason at
LOG_INFO or higher instead of LOG_DEBUG. For journalctl --header,
logging the reason at a level higher than LOG_DEBUG doesn't really
make sense. To accomodate both use cases, make the log level used
by journal_file_rotate_suggested() configurable.

src/journal/journald-server.c

@@ -819,7 +819,7 @@ static void write_to_journal(Server *s, uid_t uid, struct iovec *iovec, size_t n
                 if (!f)
                         return;
 
-                if (journal_file_rotate_suggested(f, s->max_file_usec)) {
+                if (journal_file_rotate_suggested(f, s->max_file_usec, LOG_DEBUG)) {
                         log_debug("%s: Journal header limits reached or header out-of-date, rotating.", f->path);
                         rotate = true;
                 }