cfg80211: add radiotap VHT info to rtap_namespace_sizes

Add IEEE80211_RADIOTAP_VHT entry to rtap_namespace_sizes array in order to
define alignment and size of VHT info in tx radiotap

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>