rtprtxreceive: allow passthrough and non-rtp buffers
To avoid mapping rtp buffers when RTX is not in use, and to not do a full error on receiving a non-rtp buffer, since you have no control of what a rouge sender might send you.
Due to an influx of spam, we have had to impose restrictions on new accounts. Please see this wiki page for instructions on how to get full permissions. Sorry for the inconvenience.
To avoid mapping rtp buffers when RTX is not in use, and to not do a full error on receiving a non-rtp buffer, since you have no control of what a rouge sender might send you.