target: Add internal READ_INSERT support

This patch adds READ_INSERT support in target_read_prot_action() that
invokes sbc_dif_generate() when LIO is responsible for generating the
outgoing T10-PI.

Required for supporting fabrics that exchange protection information,
and would like to function with un-protected devices.
Reviewed-by: Martin Petersen <martin.petersen@oracle.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -1994,6 +1994,12 @@ static bool target_read_prot_action(struct se_cmd *cmd)
 			}
 		}
 		break;
+	case TARGET_PROT_DIN_INSERT:
+		if (cmd->se_sess->sup_prot_ops & TARGET_PROT_DIN_INSERT)
+			break;
+
+		sbc_dif_generate(cmd);
+		break;
 	default:
 		break;
 	}