Resolve "srtserversrc yields malformed rtp payloads in 1.16"

It seems that srtsrc had the idea to merge packets if possible. This is probably not a goo idea in light of bug #1005 (closed) so instead let's do one read per instance. The next step is to use buffer lists in case there is a need for it.. But the do-timestamp code only acts on the first buffer of a bufferlist, so it may not be enough

Closes #1005 (closed)