Maybe race condition in tunnel build/close

[karalabe]

In the Erlang binding if I construct a tunnel and immediately close it down, on the remote side it usually hangs with - I think - Iris never replying to the tear-down request. This seems to be caused in the Iris node not finishing the tunnel construction but already receiving the tear-down, and loosing the close message somewhere along the way.

This should never happen as a tunnel should be fully constructed before any side receives the ack. So this needs investigation, but it seems I introduced a bug somewhere along the way.

The commit which illustrates this bug is in iris-erl 9b817dcedeb3b03bc22536e97dce6c46a84b9029