iwlwifi: convert correctly rate_n_flags to PLCP index for mimo3 packets

The driver does not properly convert rate_n_flags to PLCP index for mimo3
packets. This makes mac80211 drop the packets

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

drivers/net/wireless/iwlwifi/iwl-core.c

@@ -120,7 +120,9 @@ int iwl_hwrate_to_plcp_idx(u32 rate_n_flags)
 	if (rate_n_flags & RATE_MCS_HT_MSK) {
 		idx = (rate_n_flags & 0xff);
 
-		if (idx >= IWL_RATE_MIMO2_6M_PLCP)
+		if (idx >= IWL_RATE_MIMO3_6M_PLCP)
+			idx = idx - IWL_RATE_MIMO3_6M_PLCP;
+		else if (idx >= IWL_RATE_MIMO2_6M_PLCP)
 			idx = idx - IWL_RATE_MIMO2_6M_PLCP;
 
 		idx += IWL_FIRST_OFDM_RATE;