fix ap_bandwidth in 802.11 media specific info
The 'ap_bandwidth' field is expected to hold the channel width as an enumeration mapping to dot11CurrentChannelWidth. The field has value from this enum list: cbw20(= 0), cbw40(= 1), cbw80(= 2), cbw160(= 3), cbw80+80(= 4), cbw320(= 5).
(cherry picked from commit 46ae15e9)