Format of Function 0026h/Subfunction 0016h ("shutdown") data:
Offset	Size	Description	)
 00h	WORD	(ret) shutdown status (0000h successful, FFFFh error)
 02h  4 BYTEs	(ret) ???
 04h	WORD	(call) socket handle
 06*h	WORD	(call) what (0 = receives, 1 = sends, 2 = both)