Clear more stuff on network switch

[mrdomino]

This issue would make autonet clear things like chan and wpakey in addition to BSSID when it switches to a new profile. My current workaround is to just put -wpakey in hostname.if(5) files for open networks, but if I ever manually configure a channel, what generally happens is I forget I've done this, get confused when I can't connect to a new network, reboot, and realize what I did after everything works.