sip_session: fix for the previous patch

darcs-hash:20090330094729-b2873-3f5f802d45cc38a9ec7f78a8f48a8270431e8074
Don't wait for MSRPDidEnd in Session when stopping locally

darcs-hash:20090330095554-58103-893dc2afa41e7e6d84dcb959ca754dfdeed9bf2f