#17 Workaround for HP/Agilent 34401A

[Edward]

On some GPIB-USB-HS units, the IBGTS the driver issues before a write also clears
the controller's bus addressing, so the write fails with NIUSB_ADDRESSING_ERROR.

Tested on a Raspberry Pi against an HP/Agilent 34401A: the first and all
subsequent *IDN?, MEASure? and READ?succeed, with the workaround engaging once.

[DaveP]

Hi Edward,
Could you please check to see whether your board is a genuine NI product ? See https://sourceforge.net/p/linux-gpib/bugs/82/#4c41

I am somewhat reticent to introduce clone specific code but this too can be discussed.
cheers,
-Dave

[Edward]

It came sealed in an NI box and has the correct serial and everything, but when physically opened the adapter, there's indeed not what's supposed to be there. A CBM9002A-100 (Corebai) and a APM32F407VET6 (Geehy).

I got it working though, but indeed, the code introduced would be specific for a cloned version, not for the real NI adapter.