knfsd: Validate filehandle type in fsid_source

knfsd: Validate filehandle type in fsid_source

patch b8da0d1c27f144bce999c653467106f3f0d5a308 in mainline.

fsid_source decided where to get the 'fsid' number to
return for a GETATTR based on the type of filehandle.
It can be from the device, from the fsid, or from the
UUID.

It is possible for the filehandle to be inconsistent
with the export information, so make sure the export information
actually has the info implied by the value returned by
fsid_source.

Signed-off-by: Neil Brown <neilb@suse.de>
Cc: "Luiz Fernando N. Capitulino" <lcapitulino@gmail.com>
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oliver Pintr <oliver.pntr@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>