move definitions of channels attributes away from ieee80211.h such

move definitions of channels attributes away from ieee80211.h such
that ieee80211.h contains only definitions that are part of the
802.11 standard and not constants used internally by net80211.
because channels attributes are exported to userland through the
radiotap BPF interface, add the definitions to ieee80211_radiotap.h
too (which must be kept in sync with what is used in net80211).
also, do not export combinations of channel attributes to userland
so that noone get stupid ideas.