Add option to disable local peer discovery

[nurupo]

#296 was storing local peer discovery option in DHT, when it should be local to friend connections, as friend connections are the only ones who use LAN discovery.

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This change is 

[robinlinden]

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Reviewed 7 of 7 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[sudden6]

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Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[iphydf]

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Review status: all files reviewed at latest revision, 1 unresolved discussion, some commit checks failed.

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toxcore/Messenger.h, line 80 at r1 (raw file):

    uint16_t tcp_server_port;

    uint8_t hole_punching_enabled;

If you want, you can change this to bool as well. It's an unrelated change, so it's up to you.

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Comments from Reviewable

[jhert0]

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Reviewed 7 of 7 files at r1.
Review status: all files reviewed at latest revision, 1 unresolved discussion, some commit checks failed.

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Comments from Reviewable

[iphydf]

@GrayHatter this still needs your review - it is an API change.