Target/sbc: Set protection operation and relevant checks

SBC-3 mandates the protection checks that must be
performed in the rdprotect/wrprotect field. Use them.
According to backstore device pi_attributes and
cdb rdprotect/wrprotect field.

(Fix incorrect se_cmd->prot_type -> TARGET_PROT_NORMAL
 comparision in transport_generic_new_cmd - nab)
(Fix missing break in sbc_set_prot_op_checks - DanC + Sagi)

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>