This cleans up the network interface and removes a linear hashmap search in the network interface's priority queue.

The network interface used to need to deal with both rust and C sockets, so it stored tagged pointers for CompatSocket objects. Now that the TCP socket is the only remaining C socket, and it has a rust wrapper LegacyTcpSocket, C sockets aren't used in the network interface anymore. The network interface now only stores boxed InetSocket objects. This also allows us to remove tagged pointers from our C code.

The hashmap in the priority queue used by the fifo qdisc now uses custom hash and eq implementations, which allows us to avoid a linear search through the hashmap which used the canonical handles to identify the same socket.

The new hash function is more expensive since it uses a real hash function (DefaultHasher as used by the stdlib HashMap), whereas the original glib code doesn't seem to actually use a hash function:

https://docs.gtk.org/glib/type_func.HashTable.new.html

If hash_func is NULL, g_direct_hash() is used.

https://github.com/GNOME/glib/blob/40081f9b627904c2506b6d3837334e4ce05052da/glib/ghash.c#L2483-L2487

guint
g_direct_hash (gconstpointer v)
{
  return GPOINTER_TO_UINT (v);
}

This PR contains a lot of changes along the rust/C boundary, but everything seems to still work so hopefully it's correct.

This may fix #3238.

Edit:

There doesn't seem to be much (if any) of a performance regression. The simulation results have remained unchanged. The following are from a slightly older version of this PR, but I don't expect it would make any difference.

Edit 2: One commit was split off into #3240.