INT 7A - Novell NetWare - SPX Driver - LISTEN FOR SPX CONNECTION
        BX = 0012h
        AH = watchdog flag
            00h disabled
            01h enabled
        AL = retry count (00h = default)
        ES:SI -> Event Control Block (see BX=0003h)
Notes:  there should always be at least two SPX ECB's listening to a socket, so
          that NetWare can perform its internal packet exchanges
        this function is supported by Advanced NetWare 2.1+
SeeAlso: BX=0011h,BX=0013h,BX=0014h

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