Fixed update of local SDP in Invitation

Ignore-this: 6fb445cc50d78f7d9d173ced87a14a1e

darcs-hash:20090616152026-1e3d8-266b1b5cc233feed401ef92e3bee9cd71fd62888
Fixed SIPURI to use None for unspecified port

Ignore-this: 4242eca066ed67ace2e647ff6735f8dc

darcs-hash:20090616180311-1e3d8-b0ae2961055d9093aa982a500fa2bda6e8fd6926