Allows incoming call to be accepted even if an outgoing call is in progress. In such case, outgoing call is automatically canceled.

take local ip address for media each time a reINVITE is done, to take into account possible network changes.
remove sig_localip from LinphoneCall, that appears to be useless

This reverts commit b03c70b0.

Fix a bug in ICE where the session state was not correct when a peer added a video stream during a call and the other peer refused it.