TEST: Add a test that is cmdsn is too low the target just ignores the pdu

include/iscsi-private.h

@@ -71,6 +71,7 @@ struct iscsi_context {
 	unsigned char isid[6];
 	uint32_t itt;
 	uint32_t cmdsn;
+	uint32_t expcmdsn;
 	uint32_t maxcmdsn;
 	uint32_t statsn;
 	enum iscsi_header_digest want_header_digest;