Clean up "close socket" routines.

Clean up "close socket" routines.

We use the new rbtree DeleteOrder when walking over the packet list.
When the "eol tcp/proxy listener" callback is run, it can return
"please delete this node", instead of calling rbtree_delete.

Doing that allows the walker to be aware of deletions, unlike
before.

This turned out to make the code simpler, and the whole event fd
handling has become more robust.