iwlwifi: don't switch to SGI if not supported by AP

This patch fixes SGI support. RS didn't look at the capabilities of the AP
before switching to SGI, this should lead to a stall in the traffic with an
AP that doesn't support SGI.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Guy Cohen  <guy.cohen@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl4965-base.c b/drivers/net/wireless/iwlwifi/iwl4965-base.c
index dd2fd40..a532a9e 100644
--- a/drivers/net/wireless/iwlwifi/iwl4965-base.c
+++ b/drivers/net/wireless/iwlwifi/iwl4965-base.c
@@ -700,9 +700,9 @@
 	priv->ps_mode = (u8)((ht_conf->cap & IEEE80211_HT_CAP_MIMO_PS) >> 2);
 
 	if (ht_conf->cap & IEEE80211_HT_CAP_SGI_20)
-		iwl_conf->sgf |= 0x1;
+		iwl_conf->sgf |= HT_SHORT_GI_20MHZ;
 	if (ht_conf->cap & IEEE80211_HT_CAP_SGI_40)
-		iwl_conf->sgf |= 0x2;
+		iwl_conf->sgf |= HT_SHORT_GI_40MHZ;
 
 	iwl_conf->is_green_field = !!(ht_conf->cap & IEEE80211_HT_CAP_GRN_FLD);
 	iwl_conf->max_amsdu_size =