fanotify.7, fanotify_mark.2: Document FAN_DIR_MODIFY

fanotify.7, fanotify_mark.2: Document FAN_DIR_MODIFY

Document the details of the new FAN_DIR_MODIFY event, which
introduces entry name information to the fanotify event
reporting format.

Enhance the fanotify_fid.c example to also report this event.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>