Provides a calling process with an I/O channel, thereby allowing
    the calling process to perform I/O operations on the network
    pseudodevice.
    On Alpha and I64 systems, this service accepts 64-bit addresses.
    Format
      SYS$ASSIGN  devnam, chan, [acmode], [mbxnam], [flags]
    C Prototype
      int sys$assign  (void *devnam, unsigned short int *chan,
                      unsigned int acmode, void *mbxnam,...);
    Returns
      OpenVMS usage:cond_value
      type:         longword (unsigned)
      access:       write only
      mechanism:    by value
    Longword condition value. All system services return (by
    immediate value) a condition value in R0. Condition values that
    can be returned by this service are listed under Condition Values
    Returned.