iwlwifi: mvm: set correct chains in Rx status

ieee80211_rx_status::chains was always set to zero.
That caused rate scaling to always start with the
lowest rate possible (rs_get_initial_rate).
Set it correctly according to the MPDU response.
Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c

@@ -213,6 +213,7 @@ static void iwl_mvm_get_signal_strength(struct iwl_mvm *mvm,
 					struct ieee80211_rx_status *rx_status)
 {
 	int energy_a, energy_b, max_energy;
+	u32 rate_flags = le32_to_cpu(desc->rate_n_flags);
 
 	energy_a = desc->energy_a;
 	energy_a = energy_a ? -energy_a : S8_MIN;
@@ -224,7 +225,8 @@ static void iwl_mvm_get_signal_strength(struct iwl_mvm *mvm,
 			energy_a, energy_b, max_energy);
 
 	rx_status->signal = max_energy;
-	rx_status->chains = 0; /* TODO: phy info */
+	rx_status->chains =
+		(rate_flags & RATE_MCS_ANT_AB_MSK) >> RATE_MCS_ANT_POS;
 	rx_status->chain_signal[0] = energy_a;
 	rx_status->chain_signal[1] = energy_b;
 	rx_status->chain_signal[2] = S8_MIN;