Add configuration parameter that allows to skip discovering interfaces

[fdellwing]

This adds a new configuration parameter that allows the user to completly skip calling is_same_machine which is very expensive once the machine has a critical mass of interfaces.

This comes with the downside of having to do more work in setting up potential unnecessary binds.

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We have a server with around 10k network interfaces and current versions of sslh are absolutly unusable there.

[yrutschle]

Thanks for the contribution.
I don't remember the rationale for some of the code in that area: does your patch not affect transparent proxying?
(I'm a bit confused about how transparent proxying still works if the target is on localhost: I feel it should still need to bind the server-side connection)

[fdellwing]

We found later after more testing, that for transparent proxying on localhost we can not return there. So we need to actually skip calling is_same_machine but run the following code regardless. For this the config check could be moved into the is_same_machine function or and additional layer of if could be used. Which one do you prefer?