iwlwifi: set HT flags in ieee80211_rx_status for received packets

Add code to set the HT flags (HT, 40 MHz, Short guard interval) in
the ieee80211_rx_status field passed to mac80211.  This ensures that mac80211
processes these HT packets correctly.

Signed-off-by: Daniel C Halperin <daniel.c.halperin@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>