How to enable AP 11n mode with ST60 in openWRT

ST60 doesn't support  [HT40]  11n mode in 2.4G.

In OpenWRT, the PHY is set by adding (Logic OR) the two settings of Band-1(2.4G) and Band-2(5G).

So, [HT20] and [HT40] two modes are always set.

Need to modify the OpenWRT source so that only [HT20] is set in case of 2.4G operation of the ST60 modem.