INT 61 u - PC/TCP kernel v2.05 - "net_select" - ???
        AH = 0Eh
        BX = ???
        DS:DX -> ???
        ES:DI -> ???
Return: CF clear
        ???
Notes:  the installation check consists of testing for the signature "TCPTSR"
          three bytes beyond the start of the interrupt handler
        INT 61 is the default; PC/TCP v2.05 may be configured to use any
          interrupt from 20h through E0h
SeeAlso: INT 61/AH=00h"PC/TCP"