api: Fix a bug with parsing the 6-byte length format lba
api: Fix a bug with parsing the 6-byte length format lba

A six-byte CDB may contain a 21-bit LOGICAL BLOCK ADDRESS field.

Signed-off-by: Xiubo Li <67e5e1ee902b4e67bce18ea43d9c4b0430ce5e6c@cmss.chinamobile.com>

open-iscsi/tcmu-runner,open-iscsi/tcmu-runner,liuy/tcmu-runner,lxbsz/tcmu-runner,agrover/tcmu-runner