INT 61 - PC/TCP kernel v2.05+ - "net_write" - WRITE TO THE NETWORK
        AH = 1Ah
        BX = network descriptor
        CX = number of bytes to transmit (0000h allowed)
        DX = send options (see below)
        DS:SI -> data to be written
Return: CF clear if successful
            AX = number of bytes actually written
            DX = ???
        CF set on error
            AX = error code (see INT 61"PC/TCP")
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"PC/TCP",INT 61/AH=00h"PC/TCP",INT 61/AH=1Bh,INT 61/AH=1Ch
SeeAlso: INT 63/AH=19h"BW-TCP",INT 63/AH=1Bh"BW-TCP"

Bitfields for send options:
 bit 0  signal "URG"ent data
 bit 3  attempt rerouting on non-stream calls if first attempt fails
 bit 4  send data with PUSH flag (no override of Nagle)
        (see option 0Ch)
 bit 5  fail rather than truncating datagram
 bit 6  fail rather than blocking
 bit 7  broadcast packet

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