btl/openib/udcm: fix two race conditions

This commit fixes two nasty races:

 - One can occur if the connection request message and connection completion
   message arrive out of order. This can happen normally when adaptive routing
   is used and also in a timeout situation where a UD message is lost.

 - One occurs when handling an ack at the same time as we are handling the
   message timeout. In this case we can not free the message or the timeout
   will be operating on invalid data. This fix is a band-aid until I can come
   up with a better approach. Instead of freeing the message it is marked
   as inactive and the event callback is triggered immediately (this has no
   affect if the callback is already active). The callback then frees the
   message if it is inactive.

cmr=v1.8.1:reviewer=pasha