80211: consistently order 160 and 80+80

For flags and checks the order goes VHT160 and then VHT80P80 unless
checks are in reverse order ("more comes first") in which case we
deal with VHT80P80 first.
The one reverse order to pick out is where we check channel
prefernences. While it may seem that VHT160 is better, finding
two "free" channels (VHT 80+80) is more likely so we do prefer that.

While dealing with VHT160 and VHT80P80 add extra clauses previously
missing or marked TODO in a few places.

Reviewed by: adrian, gnn
MFC after: 2 weeks
Sponsored by: Rubicon Communications, LLC (d/b/a "Netgate")
Differential Revision: https://reviews.freebsd.org/D26002