logstate: don't log {} when tracing notifications

darcs-hash:20090428100428-b2873-ed4ea1f90669535fecc97becc8dea70a9f49f9e4
session2.add_stream: expect that the other party may zero the port

darcs-hash:20090428100638-b2873-9b76f9500c1e9c9c5148447e2e81a9aae6ab6eaa