fanotify: Add helpers to decide whether to report FID/DFID

Now that there is an event that reports FID records even for a zeroed
file handle, wrap the logic that deides whether to issue the records
into helper functions.  This shouldn't have any impact on the code, but
simplifies further patches.

Link: https://lore.kernel.org/r/20211025192746.66445-24-krisman@collabora.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>