path: drop IN_ATTRIB from parent directory watches

When watching a given pathspec, systemd unconditionally installs
IN_ATTRIB watches to track the link count of the resolved file. This
way, we are notified if the watched path disappears, even if the
resolved file inode is not removed.

Similarly, systemd installs inotify watches on each parent directory, to
be notified when the specified path appears. However, for these watches
IN_ATTRIB is an unnecessary addition to the mask. In inotify, IN_ATTRIB
on a directory is emitted whenever the attributes of any child changes,
which, for many paths, has the potential to cause a high number of
spurious wakeups in systemd. Let's remove IN_ATTRIB from the mask when
installing watches on the parent directories of the specified path.

src/core/path.c

@@ -81,7 +81,7 @@ int path_spec_watch(PathSpec *s, sd_event_io_handler_t handler) {
                         tmp = *cut;
                         *cut = '\0';
 
-                        flags = IN_MOVE_SELF | IN_DELETE_SELF | IN_ATTRIB | IN_CREATE | IN_MOVED_TO;
+                        flags = IN_MOVE_SELF | IN_DELETE_SELF | IN_CREATE | IN_MOVED_TO;
                 } else {
                         cut = NULL;
                         flags = flags_table[s->type];