Add setter methods to SocketAddr{,V4,V6}

[SimonSapin]

As demonstrated in the resolve_socket_addr change, this is less awkward than re-creating a new address from the other parts.

If this is to be accepted, pleas open a tracking issue (I can’t set the appropriate tags) and I’ll update the PR with the tracking issue number.

[rust-highfive]

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[alexcrichton]

We probably want to add set_foo accessors for all components rather than just port (e.g. ip, flowinfo, ...), but otherwise seems fine to me.

[frewsxcv]

/home/travis/build/rust-lang/rust/src/libstd/net/addr.rs:86: line longer than 100 chars
/home/travis/build/rust-lang/rust/src/libstd/net/addr.rs:122: line longer than 100 chars
/home/travis/build/rust-lang/rust/src/libstd/net/addr.rs:157: line longer than 100 chars

[SimonSapin]

All 3 of these lines are too long because of // FIXME add tracking issue which will be removed before this lands.

@alexcrichton Do you want all setters in this PR, or is that something for later?

[alexcrichton]

I'd personally prefer to have all the setters in this PR, but oops I forgot to tag this with T-libs to ensure it came up during triage.

[alexcrichton]

The libs team discussed this during triage today and the conclusion was that this is functionality that seems good to have to us.

@SimonSapin could you update with setters for the other fields (e.g. ip, flowinfo, etc) and also with a tracking issue?

[SimonSapin]

@alexcrichton done.

The only thing of note is that when SocketAddr::set_ip is called with a v4 self and a v6 new IP, flowinfo and scope_id default to zero like in SocketAddr::new. The other way around they are dropped. All in all, SocketAddr::set_ip only keeps the port number from self when the version changes.

[SimonSapin]

I thought this was not worth mentioning in the doc-comment since SocketAddr::new doesn’t either.

[alexcrichton]

@bors: r+ 3de820e

Thanks @SimonSapin! These are exactly the semantics I was expecting to have :)

[bors]

⌛ Testing commit 3de820e with merge 7342dd8...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-mac-ios-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt