Int 7C Fn 0012  - Sk-upps Data Link Interface Api - Sync Request Buffer    [N]

   AX = 0012h
   DX = protocol ID (see #3520)

Return: AX = completion code (see #3517)
   if AX=0000h: ES:BX -> Mbuf (see #3518)

Note:  If the protocol wants to be informed when an Mbuf becomes available,
     REQUEST BUFFER (AX=0004h) should be used instead.

See Also: AX=0004h,AX=0005h,AX=0006h,AX=0013h