Add an extra validation of the len parameter, as for ext4 some files
might have smaller file size limits than others.  This also means the
redundant size check in ext4_ioctl_get_es_cache can go away, as all
size checking is done in the shared fiemap handler.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20200505154324.3226743-3-hch@lst.deSigned-off-by: Theodore Ts'o <tytso@mit.edu>