mac80211: do not enable VHT in the default config on 2.4 GHz

Some drivers advertise it, but it's not supported at the moment

Reported-by: John Thomson <git@johnthomson.fastmail.com.au>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
(cherry-picked from commit 42a99b18ff)

package/kernel/mac80211/files/lib/wifi/mac80211.sh

@@ -70,7 +70,7 @@ BEGIN {
         if (channel) {
 		mode="NOHT"
 		if (ht) mode="HT20"
-		if (vht) mode="VHT80"
+		if (vht && band != "1:")) mode="VHT80"
 		if (he) mode="HE80"
 		if (he && band == "1:") mode="HE20"
                 sub("\\[", "", channel)