webrtc/receive-bin: block pads before dtlssrtpdec:

Fixes SSL errors in fast-start scenarios and whenever media stream may
be received before an answer is set.
6 jobs for webrtc-media-before-answer in 26 minutes and 53 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Preparation
passed #67331
gst indent

00:00:44

passed #67330
manifest

00:00:28

 
  Build
passed #67332
build fedora x86_64

00:02:53

 
  Test
passed #67333
check fedora

00:16:08

 
  Full Builds
passed #67334
build android arm64 api28

00:03:44

passed #67335
build cerbero fedora x86_64

00:07:06