INT 7A - Novell NetWare - IPX Driver - LISTEN FOR PACKET
        BX = 0004h
        ES:SI -> Event Control Block (see BX=0003h)
Return: AL = status
            FFh no listening socket
Desc:   this function provides IPX with an ECB for receiving an IPX packet, but
          does not wait for a packet to arrive
Notes:  the application must open a socket and initialize the ECB's ESR
          address, socket number, fragment count, and fragment descriptor
          fields before invoking this function
        there is no limit on the number of ECBs which may simultaneously be
          listening on a socket
        this function is supported by Advanced NetWare 1.02+
SeeAlso: BX=0000h,BX=0003h