mac80211: propagate STBC / LDPC flags to radiotap

This capabilities weren't propagated to the radiotap header.
We don't set here the VHT_KNOWN / MCS_HAVE flag because not
all the low level drivers will know how to properly flag
the frames, hence the low level driver will be in charge
of setting IEEE80211_RADIOTAP_MCS_HAVE_FEC,
IEEE80211_RADIOTAP_MCS_HAVE_STBC and / or
IEEE80211_RADIOTAP_VHT_KNOWN_STBC according to its
capabilities.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>