INT 61 - PC/TCP kernel v2.05+ - "net_select" - DETECT READINESS OF NETWORK
        AH = 0Eh
        BX = maximum value of network descriptor for which to return info
        DS:DX -> 32-bit (max) array of bit flags for read readiness
        ES:DI -> 32-bit (max) array of bit flags for write readiness
Return: CF clear
Notes:  bits in the DS:DX buffer are set if the corresponding network
          descriptor may be read without blocking; bits in the ES:DI buffer
          are set if the corresponding network descriptor may be written
          without blocking.  This implies that the network descriptor has
          opened correctly and the protocol initialized.
        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"PC/TCP",INT 61/AH=00h"PC/TCP"

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