As suggested on the Arma 3 tracker, this issue has been submitted to Qualcomm Atheros as well.

Hi, thanks for reply. It has been done.

The following below is the reply from Qualcomm Atheros that solved the problem. Saying that it is likley "the application won't accept the offload features of the Killer" kinda implies an error in the Arma 3 code. But it seems to only affect Gigabyte motherboards. That should make it a Gigabyte problem.

I suppose the ticket could be closed on that point, unless BIS want to take further actions.

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Here's the solution.

The problem is likely that the application won't accept the offload features of the Killer, so you may need to bypass it. You can do that by making sure that you're running the latest version of the drivers (from http://www.qca.qualcomm.com/resources/driverdownloads/) and do the following:

First, ensure hidden files and folders are being shown in Windows Explorer, then navigate to C:\ProgramData\Bigfoot Networks

Right-click the GameDetect.xml file and click "Edit"

From here, you'll see a section at the top that looks like this:

<GameDetectSettings>
<ByPassSection>
<ByPass>mozybackup.exe</ByPass>
<ByPass>mozystat.exe</ByPass>
<ByPass>mozyconfig.exe</ByPass>

All you need to do is add a new line right under the mozy stuff and replace it with your application .exe. So, it should look something like this:
<ByPass>yourapp.exe</ByPass>
Then save the file and exit, then you'll need to reboot. You may then be able to connect to your game.