[wlan] Activate IEEE 802.11ac VHT

Fuchsia enters a new level of WLAN connectivity by supporting
IEEE 802.11ac VHT, up to 80 MHz bandwidth. The PHY speed will be 867 Mbps.

This effect goes to the platforms using softmac WLAN
device drivers, up to the chipset capability. That is,
 - ath10k-based platforms will use up to 802.11ac VHT
 - ralink-based platforms will continue to use up to 802.11n HT
 - brcmfmac-based platforms will continue its autonomous operation,
   up to 802.11ac VHT

Test: Smoking 4 major platforms against 8 major brand and models of APs
      More details are to be shared offline.
NET-1141

Change-Id: Idbb2d562f67dc75c5ab9dbabad407ca9f5f21be1
1 file changed