[tcp] Connection State is Never Cleaned Up

[gatoWololo]

The Inner struct for TcpPeer holds the established connections on the established: HashMap<(Ipv4Endpoint, Ipv4Endpoint), EstablishedSocket<RT>> field. It seems the remove method is never called on this HashMap. So while the socket state is updated, the established socket is never cleaned up.

At some point this state should probably be cleared from established.