LinuxKPI: 80211: implement (*get_antenna) and set ic_[rt]xstream

Implement the mac80211 (*get_antenna) call and after checking any
antenna information present query the current configuration on startup
(both informations should be identical at this point in theory).
Both the wiphy variables and function call report a bitmask not a count.
Count the bits for net80211 for as long as we get away with just a
number in ic_[rt]xstream.

Sponsored by: The FreeBSD Foundation
MFC after: 4 days