isofs: support full length file names (255 instead of 253)

isofs: support full length file names (255 instead of 253)

Linux file names are in principle limited only to PATH_MAX (which is
4096) but the code in get_rock_ridge_filename() limits them to 253
characters.

As mentioned by Jan Kara, the Rockridge standard to ECMA119/ISO9660 has
no limit of file name length, but this limits file names to the
traditional 255 NAME_MAX value.

Signed-off-by: Shawn Landden <slandden@gmail.com>
Link: https://patch.msgid.link/CA+49okq0ouJvAx0=txR_gyNKtZj55p3Zw4MB8jXZsGr4bEGjRA@mail.gmail.com
Signed-off-by: Jan Kara <jack@suse.cz>