Add TcpSocket methods to set reuseport and reuseaddr to UdpSocket

[reconbot]

Is your feature request related to a problem? Please describe.
I'm working on porting an existing udp multicast based application to rust and I need to to be able to have multiple versions of the program reading from the same port in a multicast session. (Made possible by reuseaddr with udp and multicast)

Describe the solution you'd like
These methods exist for TcpSocket and I'd like to see them on UdpSocket

Describe alternatives you've considered
I hear its possible to bind a socket and give it to tokio. I have found some comments in the source and some github issues to this effect but I haven't found documentation.

Additional context

• net: expose more socket options on TcpSocket #3082 asking for this for tcp sockets
• net: Add get/set reuseport and get_localaddr/reuseaddr for TcpSocket #3083 implementing it for tcp sockets

[Noah-Kennedy]

The preferred way to do this is to use socket2

[reconbot]

Why have it inconsistent though?

[Darksonn]

If we expose them for TcpSocket, then I guess it's fine to also do so for UdpSocket.

[Noah-Kennedy]

I agree, it's just a matter of finding a way to make the semantics work well here. Do these need to be enabled before binding? I can't recall.

[reconbot]

Osx needs it before. I recall the answer for linux is "it depends".

I can see why we'd suggest using socket2 as it's not possible to do that with the bind api.