net80211: return 80P80 before 160

In ieee80211_vht_get_chwidth_ie() we need to return 80P80 (3) before
VHT160 (2) as otherwise we'll never use 80P80. Fix the order.

MFC after: 2 weeks
X-MFC with: r364303 (which missed this)
Sponsored by: Rubicon Communications, LLC (d/b/a "Netgate")