It seems that PacketSocket::Close doesn't work properly for me - I 
kept getting segfaults when packets are attempted to be forwarded 
through closed sockets that had already had the memory deallocated.

During a typical lifetime of a PacketSocket, the protocal handler is registered in the function PacketSocket::DoBind, executed on transiting from STATE_OPEN to STATE_BOUND. When transiting from STATE_BOUND to STATE_CONNECTED, the protocol remains registered. In order to clean up properly, the PacketSocket should unregister the protocol handler on close for the transitions STATE_BOUND->STATE_CLOSED and STATE_CONNECTED->STATE_CLOSED.

Platform and version: NS-3.7 on Linux 2.6.31-14 (amd64), gcc 4.4.1

Have not developed test code to reproduce the segfault.