SSC: mode select overhaul

Fix MODE SELECT (6 & 10 byte version) to reflect T10 spec.

Incorrect behaviour reported by Sebastian Herbszt <herbszt@gmx.de>
Incorrect behaviour reported by Sunding Wei <swei@dingding.me>

Signed-off-by: Mark Harvey <markh794@gmail.com>
vtltape: Simplifiy logic for detecting correct compression routine

Split the no-compression into it's own function to stream-line
'if' statements in compression routines.

Signed-off-by: Mark Harvey <markh794@gmail.com>
vtltape: wrap duplicate code into common function - setup_crypto()

Signed-off-by: Mark Harvey <markh794@gmail.com>