INT 61 - PC/TCP kernel v2.05+ - "net_read" - READ FROM THE NETWORK
        AH = 1Bh
        BX = network descriptor
        CX = maximum number of bytes to read
        DX = receive options (see below)
        DS:SI -> buffer for data
        ES:DI -> "addr" structure (see AH=13h) for remote from which to read
                0000h:0000h for any
Return: CF clear if successful
            AX = number of bytes actually read
            DX = ???
        CF set on error
            AX = error code (see INT 61"PC/TCP")
SeeAlso: INT 61"PC/TCP",INT 61/AH=00h"PC/TCP",INT 61/AH=1Ah,INT 61/AH=1Dh

Bitfields for receive options:
 bit 1  do not remove data from queue, just copy it
 bit 2  do not copy data, just remove it from queue
 bit 5  fail if datagram would be truncated
 bit 6  do not block, return error if no data available
Note:   special case for UDP: if both bits 1 and 2 set, return num of datagrams

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