Interrupt 5Ch   NETBIOS interface entry port 
		ES:BX   pointer to network control block 
return  AL      error code (0 if none) 
note 1) When the NETBIOS is installed, Int\13 and Int\17 are interrupted by
        the NETBIOS; Int\18 is moved to Int\86 and one of Int\2 or
        Int\3 is used by NETBIOS. Also, NETBIOS extends the Int\15f\90 and
        Int\15f\91 functions (scheduler functions)
     2) Normally not initialized. 
     3) TOPS network card uses DMA 1, 3 or none.