Switch the default firmware for npe(4) from the QOS_VLAN one to the
plain-vanilla ETH microcode. The QOS_VLAN firmware added support in microcode
for handling IEEE 802.1q tags, but the npe(4) driver did not actually
support the relevant signalling. As a result, it was impossible to use
VLANs with npe(4). Switching to the more basic microcode (same license)
removes the on-NIC promisisng and makes vlan(4) work on both NPE interfaces.

Ref: https://lists.freebsd.org/pipermail/freebsd-arm/2012-August/003826.html