sipvoiplink: avoid to drop rotation's informations

if videoRtp is not initialized, the information is dropped. So,
it should be stored to avoid any drop of informations.
Note: in the future the container should change, because rotation
is currently applied to all video streams.

Change-Id: I036ffe7b6a248a3d8d7defeff1be78e008447fbd
GitLab: #678