Int 6A Fn 03  - Decnet DOS Local Area Transport - Status                   [N]

   AH = 03h
   DH = FFh
   DL = handle

Return: AH = status flags (see below)

Bitfields for status flags:
 bit 5 transmit buffer empty
 bit 3 session in start state
 bit 2 session not active
 bit 1 unable to queue transmit data
 bit 0 receive data available