Onlined should do less aggressive checking

[matthijs]

Right now, onlined does fairly aggressive checking (ping every 10 seconds, increased to every second when the connection fails). This used to make sense when onlined controlled the orange screen (you would want to get rid of that as soon as possible), but now onlined only controls the hotspot status, it should be a bit less aggresive (ideally, it would do some kind of backoff, reducing the frequency of pings when the Fonera is offline for a longer period).

[matthijs]

#1129 is a duplicate.

[matthijs]

(In [2073]) onlined: Test by doing a DNS lookup instead of an HTTP request.

Since onlined is not as important as it used to be, but still causes a significant load on the fon webserver, doing just a DNS lookup should be sufficient. This reduce the load and shift distribute it over the DNS servers of all users' ISPs, making the resulting load negligable.

There is a small change of this causing false positives, i.e. the Fonera thinking it is online when it isn't, when for some reason DNS works but connecting to the rest of the internet doesn't. This should be acceptable.

References: #1125

[matthijs]

(In [2074]) onlined: perform checks less often.

While the Fonera is online, onlined only checks every 60 seconds (instead of 10) now. When the Fonera is offline, the Fonera still checks every second at first, but after a minute it switches to checking every two seconds, then after another minute it checks every four seconds, up to checking every 64 seconds.

Closes: #1125

[matthijs]

(In [2075]) onlined: Don't daemonize, luci.services will take care of that.

When onlined would daemonize itself, luci.services would store the wrong pid, so it could not stop onlined (so a restart would spawn a second instance).

References: #1125

[matthijs]

(In [2077]) fonbase: Restart onlined when the wan cable is (un)plugged.

This causes onlined to start checking the connection right away, instead of waiting for its regular delay interval (which can be up to a minute).

References: #1125

[matthijs]

(In [2128]) onlined: Check www.fon.com instead of updates.fon.com

This hostname will probably always remain available, while the latter could (in theory) be removed at some point.

References: #1125