net/wsconn: accept a remote addr string and plumb it through

This makes wsconn.Conns somewhat present reasonably when they are
the client of an http.Request, rather than just put a placeholder
in that field.

Updates tailscale/corp#13777

Signed-off-by: David Anderson <danderson@tailscale.com>

cmd/derper/websocket.go

@@ -50,7 +50,7 @@ func addWebSocketSupport(s *derp.Server, base http.Handler) http.Handler {
 			return
 		}
 		counterWebSocketAccepts.Add(1)
-		wc := wsconn.NetConn(r.Context(), c, websocket.MessageBinary)
+		wc := wsconn.NetConn(r.Context(), c, websocket.MessageBinary, r.RemoteAddr)
 		brw := bufio.NewReadWriter(bufio.NewReader(wc), bufio.NewWriter(wc))
 		s.Accept(r.Context(), wc, brw, r.RemoteAddr)
 	})