Add support for SO_REUSEADDR socket address

[cipriancraciun]

By default, at least on Linux, if I start catflap, then kill it and start it again (within a few seconds), it fails with Could not bind: EADDRINUSE: Address already in use, although there isn't any process actually listening on that endpoint (as confirmed by netstat); this is because the TCP/IP stack on Linux disallows the usage of the same endpoint for a time if any "delayed" packets might be received.

In order to allow the immediate restart of catflap, the SO_REUSEADDR socket address must be set when creating the socket. (This would be perhaps useful by default given that catflap is mainly meant for development purposes.)

(If accepted I'm willing to provide the patch.)

[passcod]

Would merge a patch on this too! except may as well do it outright and don't even add an option to disable, unless there's a downside?

[cipriancraciun]

[...] don't even add an option to disable, unless there's a downside?

To my knowledge there is no downside. (In all tools I've written, and in all production servers, I always configure the SO_REUSEADDR option.)

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However I think this option is not accessible on all operating systems. How should I handle this? (I could add that option only on Linux.)

[passcod]

Wherever it compiles, and if that's only linux then sure.