fsm-listen-darwin: ignore FSEvents caused by xattr changes on macOS

fsm-listen-darwin: ignore FSEvents caused by xattr changes on macOS

Ignore FSEvents resulting from `xattr` changes.  Git does not care about
xattr's or changes to xattr's, so don't waste time collecting these
events in the daemon nor transmitting them to clients.

Various security tools add xattrs to files and/or directories, such as
to mark them as having been downloaded.  We should ignore these events
since it doesn't affect the content of the file/directory or the normal
meta-data that Git cares about.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>