staging: wfx: ensure that retry policy always fallbacks to MCS0 / 1Mbps

When not using HT mode, minstrel always includes 1Mbps as fallback rate.
But, when using HT mode, this fallback is not included. Yet, it seems
that it could save some frames. So, this patch add it unconditionally.
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191217161318.31402-8-Jerome.Pouiller@silabs.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/data_tx.c

@@ -538,6 +538,17 @@ static void wfx_tx_fixup_rates(struct ieee80211_tx_rate *rates)
 			}
 		}
 	} while (!finished);
+	// Ensure that MCS0 or 1Mbps is present at the end of the retry list
+	for (i = 0; i < IEEE80211_TX_MAX_RATES; i++) {
+		if (rates[i].idx == 0)
+			break;
+		if (rates[i].idx == -1) {
+			rates[i].idx = 0;
+			rates[i].count = 8; // == hw->max_rate_tries
+			rates[i].flags = rates[i - 1].flags & IEEE80211_TX_RC_MCS;
+			break;
+		}
+	}
 	// All retries use long GI
 	for (i = 1; i < IEEE80211_TX_MAX_RATES; i++)
 		rates[i].flags &= ~IEEE80211_TX_RC_SHORT_GI;