rtspsrc: use the correct segment seqnum

8 jobs for <span class="ref-name">seqnums</span> in 12 minutes and 44 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Preparation
passed #98420
gst indent

00:00:28

passed #98419
manifest

00:00:18

 
  Build
passed #98421
build fedora x86_64

00:02:47

 
  Test
passed #98422
check fedora

00:03:32

 
  Full Builds
passed #98423
build android arm64 api28

00:03:08

passed #98425
build cerbero cross win32

00:05:00

passed #98426
build cerbero cross win64

00:05:55

passed #98424
build cerbero fedora x86_64

00:05:25