fsnotify: Add helper to detect overflow_event

Similarly to fanotify_is_perm_event and friends, provide a helper
predicate to say whether a mask is of an overflow event.

Link: https://lore.kernel.org/r/20211025192746.66445-9-krisman@collabora.com


Suggested-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Jan Kara <jack@suse.cz>