target: Ensure sess_prot_type is saved across session restart

The following incremental patch saves the current sess_prot_type into
se_node_acl, and will always reset sess_prot_type if a previous saved
value exists.  So the PI setting for the fabric's session with backend
devices not supporting PI is persistent across session restart.

(Fix se_node_acl dereference for discovery sessions - DanCarpenter)

Reviewed-by: Martin Petersen <martin.petersen@oracle.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

include/target/target_core_base.h

@@ -589,6 +589,7 @@ struct se_node_acl {
 	bool			acl_stop:1;
 	u32			queue_depth;
 	u32			acl_index;
+	enum target_prot_type	saved_prot_type;
 #define MAX_ACL_TAG_SIZE 64
 	char			acl_tag[MAX_ACL_TAG_SIZE];
 	/* Used for PR SPEC_I_PT=1 and REGISTER_AND_MOVE */