cfg80211: a reg rule is invalid if freq diff is 0

A regulatory rule is invalid when the frequency difference
between the end of the frequency range and the start is 0.
Signed-off-by: NLuis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/wireless/reg.c

@@ -321,7 +321,7 @@ static bool is_valid_reg_rule(const struct ieee80211_reg_rule *rule)
 
 	freq_diff = freq_range->end_freq_khz - freq_range->start_freq_khz;
 
-	if (freq_range->max_bandwidth_khz > freq_diff)
+	if (freq_diff <= 0 || freq_range->max_bandwidth_khz > freq_diff)
 		return false;
 
 	return true;