Revert "cfg80211: Use 5MHz bandwidth by default when checking usable channels"

This reverts commit 8eca1fb6.

Felix notes that this broke regulatory, leaving channel 12 open for AP
operation in the US regulatory domain where it isn't permitted.

Link: http://mid.gmane.org/53A6C0FF.9090104@openwrt.orgReported-by: NFelix Fietkau <nbd@openwrt.org>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/wireless/reg.c

@@ -935,7 +935,7 @@ freq_reg_info_regd(struct wiphy *wiphy, u32 center_freq,
 		if (!band_rule_found)
 			band_rule_found = freq_in_rule_band(fr, center_freq);
 
-		bw_fits = reg_does_bw_fit(fr, center_freq, MHZ_TO_KHZ(5));
+		bw_fits = reg_does_bw_fit(fr, center_freq, MHZ_TO_KHZ(20));
 
 		if (band_rule_found && bw_fits)
 			return rr;
@@ -1019,10 +1019,10 @@ static void chan_reg_rule_print_dbg(const struct ieee80211_regdomain *regd,
 }
 #endif
 
-/* Find an ieee80211_reg_rule such that a 5MHz channel with frequency
- * chan->center_freq fits there.
- * If there is no such reg_rule, disable the channel, otherwise set the
- * flags corresponding to the bandwidths allowed in the particular reg_rule
+/*
+ * Note that right now we assume the desired channel bandwidth
+ * is always 20 MHz for each individual channel (HT40 uses 20 MHz
+ * per channel, the primary and the extension channel).
  */
 static void handle_channel(struct wiphy *wiphy,
 			   enum nl80211_reg_initiator initiator,
@@ -1083,12 +1083,8 @@ static void handle_channel(struct wiphy *wiphy,
 	if (reg_rule->flags & NL80211_RRF_AUTO_BW)
 		max_bandwidth_khz = reg_get_max_bandwidth(regd, reg_rule);
 
-	if (max_bandwidth_khz < MHZ_TO_KHZ(10))
-		bw_flags = IEEE80211_CHAN_NO_10MHZ;
-	if (max_bandwidth_khz < MHZ_TO_KHZ(20))
-		bw_flags |= IEEE80211_CHAN_NO_20MHZ;
 	if (max_bandwidth_khz < MHZ_TO_KHZ(40))
-		bw_flags |= IEEE80211_CHAN_NO_HT40;
+		bw_flags = IEEE80211_CHAN_NO_HT40;
 	if (max_bandwidth_khz < MHZ_TO_KHZ(80))
 		bw_flags |= IEEE80211_CHAN_NO_80MHZ;
 	if (max_bandwidth_khz < MHZ_TO_KHZ(160))
@@ -1522,12 +1518,8 @@ static void handle_channel_custom(struct wiphy *wiphy,
 	if (reg_rule->flags & NL80211_RRF_AUTO_BW)
 		max_bandwidth_khz = reg_get_max_bandwidth(regd, reg_rule);
 
-	if (max_bandwidth_khz < MHZ_TO_KHZ(10))
-		bw_flags = IEEE80211_CHAN_NO_10MHZ;
-	if (max_bandwidth_khz < MHZ_TO_KHZ(20))
-		bw_flags |= IEEE80211_CHAN_NO_20MHZ;
 	if (max_bandwidth_khz < MHZ_TO_KHZ(40))
-		bw_flags |= IEEE80211_CHAN_NO_HT40;
+		bw_flags = IEEE80211_CHAN_NO_HT40;
 	if (max_bandwidth_khz < MHZ_TO_KHZ(80))
 		bw_flags |= IEEE80211_CHAN_NO_80MHZ;
 	if (max_bandwidth_khz < MHZ_TO_KHZ(160))