This object represents the channel extension
offset. The semantics are as follows.
noExtension - No extension channel is present and
the radio operates in the 20MHz mode.
extensionAbove - The extension channel is above the
control channel. This is applicable only if the
radio operates in the 40MHz mode.
extensionBelow - The extension channel is below the
control channel. This is applicable only if the
radio operates in the 40MHz mode.