websocket: record X-Real-IP header

[magik6k]

We currently don't support TLS here, so a reverse proxy needs to be set up, which has the side effect of loosing real ip addresses in ipfs swarm peers.

We could check if the X-Real-IP header is set when accepting connections and change the ip address we report as the remote (and probably only do that when we proxy from localhost)

[Jorropo]

That also should come with a way to set trusted reverse proxy because else someone could do a real ws conn with a X-Real-IP and change his ip to someone else for you. (the reverse proxy would be an ip or ip range (/ip4/127.0.0.1 by default) and if the connection is made via here we can know X-Real-IP should be real)

[MarcoPolo]

Here's how I think we could implement this:

• Add option to always trust this header
• By default, trust this header only of private network/localhost