iscsi-target: add void (*iscsit_release_cmd)()

Add void (*iscsit_release_cmd)() to
struct iscsit_transport, iscsi-target
uses this callback to release transport
driver resources associated with an iSCSI cmd.

cxgbit.ko needs this callback to release DDP
resource and sg page in case of
PASSTHROUGH_SG_TO_MEM_NOALLOC.

Signed-off-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/iscsi/iscsi_target_util.c b/drivers/target/iscsi/iscsi_target_util.c
index 428b0d9..a533017 100644
--- a/drivers/target/iscsi/iscsi_target_util.c
+++ b/drivers/target/iscsi/iscsi_target_util.c
@@ -725,6 +725,9 @@
 		iscsit_remove_cmd_from_immediate_queue(cmd, conn);
 		iscsit_remove_cmd_from_response_queue(cmd, conn);
 	}
+
+	if (conn && conn->conn_transport->iscsit_release_cmd)
+		conn->conn_transport->iscsit_release_cmd(conn, cmd);
 }
 
 void iscsit_free_cmd(struct iscsi_cmd *cmd, bool shutdown)