Protection against early RTCP packets.

When receiving RTCP packets early the funnel is not ready yet and
GST_FLOW_FLUSHING will be returned when pushing data to it's srcpad.
This causes the thread that handle RTCP packets to go to pause mode.
Since this thread is in pause mode there will be no further callbacks to
handle keep-alive for incoming RTCP packets. This will make the session
time out if the client is not using another keep-alive mechanism.

Change-Id: Idb29db05f59c06423fa693a2aeeacbe3a1883fc5
Part-of: <!211>
30 jobs for master in 10 minutes and 15 seconds (queued for 10 seconds)
Status Name Job ID Coverage
  Build Docker
passed alpine amd64 manifest builder docker #11512899

00:00:29

passed android docker #11512898

00:00:29

passed cerbero fedora amd64 docker #11512897

00:00:29

passed fedora amd64 docker #11512896

00:09:50

passed gst-indent amd64 docker #11512900

00:00:29

passed windows amd64 docker #11512901
windows shell 1809

00:01:05

 
  Preparation
passed gst indent #11512903

00:00:24

manual manifest #11512902
manual
 
  Build
created build cerbero cross-android universal #11512912
gstreamer
created build cerbero cross-ios universal #11512916
gst-ios-14.3
created build cerbero cross win32 #11512913
gstreamer
created build cerbero cross win64 #11512914
gstreamer
created build cerbero fedora x86_64 #11512911
gstreamer
created build cerbero macos x86_64 #11512915
gst-macos-11.1
created build cerbero msvc x86_64 #11512917
docker windows gstreamer-windows 1809
created build clang fedora x86_64 #11512907
created build msys2 #11512910
docker windows 1809 allowed to fail manual
created build nodebug fedora x86_64 #11512904
created build static fedora x86_64 #11512905
created build static nodebug fedora x86_64 #11512906
created build vs2017 amd64 #11512908
docker windows 1809
created build vs2017 x86 #11512909
docker windows 1809
 
  Test
created check fedora #11512918
gstreamer
created integration testsuites fedora 1/4 #11512919
gstreamer
created integration testsuites fedora 2/4 #11512920
gstreamer
created integration testsuites fedora 3/4 #11512921
gstreamer
created integration testsuites fedora 4/4 #11512922
gstreamer
 
  Integrate
created cross-android universal examples #11512923
created cross-ios universal examples #11512925
gst-ios-14.3
created documentation #11512924