arge(4): flip this on for AR9344 SoCs.

I couldn't test arge0->arge1 bridging, only arge0 VLAN bridging.
The DIR-825C1 only hooks up arge0 to the switch GMAC0 and so
you need to abuse VLANs to test.

Tested:

• DIR-825C1 (AR9344)