ap: sigusr1 when vtun is up to start depending services (hostapd and dhclient)
ap: create bridge per ssid
ap: decouple hostapd init from vtund init

hostapd is started per physical wlan interface, vtund per ssid
ap: support multiple ssids
ap: daemonize dhclient rightaway to ensure it writes its pidfile
ap: read with <<< instead of piping to subshell
ap: misc refactorings
ap: remove channel config for now
ap: support multiple interfaces
ap: provide explicit bssids