Removed a race condition

During bootup, the wpa-roam directive in /etc/network/interfaces
would cause wpa_supplicant to start up and try to connect to wifi
networks via wlan0. Once it decided it could not find anything
it would take device down - although it was already configured
by netconnectd. Thus the device would hang around without an ip
address, and depending on if that down taking would happen before
or after the attempt to start up dnsmasq, dnsmasq would not even
start claiming that wlan0 was not there.