refactoring conn audit, add session_id (both session_id and conn_id on

sever side), use session_id instead of conn_id for client id, and remove
conn_id in protobuf

src/client/io_loop.rs

@@ -1415,11 +1415,8 @@ impl<T: InvokeUiSession> Remote<T> {
                         }
                     }
                 }
-                Some(message::Union::PeerInfo(pi)) => match pi.conn_id {
-                    crate::SYNC_PEER_INFO_DISPLAYS => {
-                        self.handler.set_displays(&pi.displays);
-                    }
-                    _ => {}
+                Some(message::Union::PeerInfo(pi)) => {
+                    self.handler.set_displays(&pi.displays);
                 },
                 _ => {}
             }