target/sbc: Add P_TYPE + PROT_EN bits to READ_CAPACITY_16

This patch updates sbc_emulate_readcapacity_16() to set
P_TYPE and PROT_EN bits when DIF emulation is enabled by
the backend device.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>