INT 7A - Novell NetWare - IPX Driver - OPEN SOCKET
        BX = 0000h
        AL = socket longevity
            00h open until close or terminate
            FFh open until close
        DX = socket number (high byte in DL)
            0000h dynamic allocation
            else  socket to open
                0452h Service Advertising Socket
                0456h diagnostics
                4000h-7FFFh used for dynamic allocation
                8000h-FFFFh assigned by Novell
Return: AL = return code
            00h success
                DX = socket number
            FEh socket table full
            FFh socket already open
Notes:  TSRs which need to use sockets should set AL to FFh, non-resident
          programs should normally use AL=00h
        IPX can be configured to support up to 150 open sockets on a
          workstation, and defaults to 20
        this function is supported by Advanced NetWare 1.02+
SeeAlso: BX=0001h,BX=0004h