Improve LAN discovery

[Diadlo]

Issue: If another tox instance started on the not default port, LAN
discovery will be failed.

Now tox will iterate though all possible ports to find another tox
instances.

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This change is 

[Diadlo]

This change, reques update the spec
Also, I thought about trying two ports: default and incremented (any suggestions?)

[im-grey]

This is great news.

[zoff99]

@Diadlo can you please also add logging to that, so that if LAN discovery finds something this fact is logged

[Diadlo]

@zoff99 Because LAN discovery uses broadcast messages, I only can handle when someone found you, but not when you found someone

[zoff99]

@Diadlo that sounds good. with logging i can actually try it on my LAN with 2 clients and see if it works.

because now there is no logging like that, and i think its not working on my LAN.
also could it be true that a LAN node has always less "priority" than a normal node, and then the internet route would be always preferred? (thats how it feels like in my LAN)

[zoff99]

https://github.com/TokTok/spec/blob/master/spec.md#lan-discovery
"When enabled, toxcore sends these packets every 10 seconds to keep delays low"

does that mean with landiscovery "ON" packets will be sent every 10 seconds forever? or will this stop at some point?
(thinking about mobile devices again)

[zoff99]

Reviewed 2 of 2 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable

[zoff99]

does this only scan from "TOX_PORTRANGE_FROM 33445" to "TOX_PORTRANGE_TO 33545" ?

[zoff99]

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Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable

[Diadlo]

@zoff99 Added logging

does this only scan from "TOX_PORTRANGE_FROM 33445" to "TOX_PORTRANGE_TO 33545" ?

Yes

I thought about trying two ports: default and incremented

What do you think about it?

[zoff99]

@Diadlo what is "incremented" port ?

[Diadlo]

@zoff99

send_LANdiscovery(net_htons(TOX_PORT_DEFAULT), fr_c->dht);
for (uint16_t port = first; port < last; port++) {
    send_LANdiscovery(net_htons(port), fr_c->dht);
}

[robinlinden]

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Reviewed 1 of 2 files at r1, 1 of 1 files at r2, 1 of 1 files at r3.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable

[iphydf]

Rebase (or checkbox).

[Diadlo]

@iphydf Done (both)