LinuxKPI: rather than manually defining a value use the net80211 define

Define cfg80211 IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK to
net80211 IEEE80211_VHTCAP_SUPP_CHAN_WIDTH_MASK.

We should likely at some point make a sweep and replace all the
values with the defines from the comments for the matching net80211
version.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days