wifi: mac80211: ethtool: add monitor channel reporting

When running ethtool on a monitor interface, the channel
wasn't reporting properly. This adds logic to properly report
the channel for monitor interfaces in ethtool.

Signed-off-by: Dylan Eskew <dylan.eskew@candelatech.com>
Link: https://patch.msgid.link/20241113144608.334060-1-dylan.eskew@candelatech.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>