WifiStateChangeService: exit after trying for 2 minutes

It was tried until it got an IP address, but that will only happen if there
is a wifi device configured.  Since WifiStateChangeService is started when
F-Droid starts, WifiStateChangeService could run for days if someone never
connected to WiFi in that time.

WifiStateChangeService is also started by NETWORK_STATE_CHANGED_ACTION so
it should start each time there is a change to the WiFi connection.