Format of APPC/PC "Test" control block:
Offset	Size	Description	)
 00h 12 BYTEs	reserved
 0Ch	WORD	1200h (verb "Test" or "MC_Test")
 0Eh	BYTE	1 if MC_ (mapped conversation) form of verb
		0 if basic verb
 0Fh  5 BYTEs	reserved (0)
 14h	WORD	(big-endian) primary return code (see #03681)
 16h	DWORD	(big-endian) error code (see #03682)
 1Ah  8 BYTEs	(big-endian) TP_ID
 22h	DWORD	(big-endian) conversation ID
 26h	BYTE	(MC_Test only) test (0=posted, 1=request_to_send received)
Note:	error code has different interpretations for:
	0 posted data
	1 posted not data (primary return code = 0)
	1 bad TP_ID (primary return code = 1)