conf-parser: only read the first found main config file

Follow-up for 93f1da4556
and 8ea288db01

Before the offending commits, we only read the first found
main config file. If the main config file is symlinked to/as
a drop-in, we should break instead of continuing, for it to
be read later.

src/shared/conf-parser.c

@@ -557,7 +557,7 @@ static int config_parse_many_files(
 
                         if (set_contains(inodes, &st)) {
                                 log_debug("%s: symlink to/symlinked as drop-in, will be read later.", *fn);
-                                continue;
+                                break;
                         }
                 }
 
@@ -571,6 +571,8 @@ static int config_parse_many_files(
                         if (r < 0)
                                 return r;
                 }
+
+                break;
         }
 
         /* Then read all the drop-ins. */