install: follow config_path symlink (#3362)

Under NixOS, the config_path /etc/systemd/system is a symlink to
/etc/static/systemd/system. Commands such as `systemctl list-unit-files`
and `systemctl is-enabled` did not work as the symlink was not followed.

This does not affect how symlinks are treated within the config_path
directory.

src/shared/install.c

@@ -777,7 +777,7 @@ static int find_symlinks(
         assert(config_path);
         assert(same_name_link);
 
-        fd = open(config_path, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW);
+        fd = open(config_path, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC);
         if (fd < 0) {
                 if (IN_SET(errno, ENOENT, ENOTDIR, EACCES))
                         return 0;