* When receiving a #LinphoneCallUpdatedByRemote state notification, prevent LinphoneCore from performing an automatic answer.
*
* When receiving a #LinphoneCallUpdatedByRemote state notification (ie an incoming reINVITE), the default behaviour of
* LinphoneCore is defined by the "defer_update_default" option of the "sip" section of the config. If this option is 0 (the default)
* then the LinphoneCore automatically answers the reINIVTE with call parameters unchanged.
* However when for example when the remote party updated the call to propose a video stream, it can be useful
* to prompt the user before answering. This can be achieved by calling linphone_core_defer_call_update() during
* the call state notification, to deactivate the automatic answer that would just confirm the audio but reject the video.
* Then, when the user responds to dialog prompt, it becomes possible to call linphone_call_accept_update() to answer
* the reINVITE, with eventually video enabled in the LinphoneCallParams argument.
*
* The #LinphoneCallUpdatedByRemote notification can also arrive when receiving an INVITE without SDP. In such case, an unchanged offer is made
* in the 200Ok, and when the ACK containing the SDP answer is received, #LinphoneCallUpdatedByRemote is triggered to notify the application of possible
* changes in the media session. However in such case defering the update has no meaning since we just generating an offer.
*
* @param[in] call A LinphoneCall object
* @return 0 if successful, -1 if the linphone_call_defer_update() was done outside a valid #LinphoneCallUpdatedByRemote notification