rtspsrc: avoid seek DISCONT when only rate changes in same direction

Not setting DISCONT avoids a noticable delay when seeking
with only rate changing, in the same direction as current
rate.
25 jobs for ffwd_no_discont in 42 minutes and 50 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #599844
gst indent

00:00:28

passed #599843
manifest

00:00:43

 
  Build
passed #599854
build cerbero cross-android universal

00:13:07

manual #599858
gst-ios-12.2 allowed to fail manual
build cerbero cross-ios universal
passed #599855
build cerbero cross win32

00:09:40

passed #599856
build cerbero cross win64

00:09:09

passed #599853
build cerbero fedora x86_64

00:07:24

passed #599857
gst-macos-10.14
build cerbero macos x86_64

00:08:49

passed #599849
build clang fedora x86_64

00:09:00

passed #599845
build fedora x86_64

00:06:23

passed #599993
docker windows 1607
build msys2

00:11:25

passed #599846
build nodebug fedora x86_64

00:04:58

passed #599847
build static fedora x86_64

00:13:26

passed #599848
build static nodebug fedora x86_64

00:04:47

passed #599850
docker windows 1607
build vs2017 amd64

00:08:49

passed #599851
docker windows 1607
build vs2017 x86

00:09:04

failed #599852
docker windows 1607
build msys2

00:00:06

 
  Test
passed #599859
check fedora

00:04:40

passed #599860
integration testsuites fedora

00:17:09

passed #599862
valgrind bad

00:08:36

passed #599863
valgrind ges

00:08:14

passed #599861
valgrind good

00:10:38

 
  Integrate
passed #599864
cross-android universal examples

00:09:26

manual #599866
gst-ios-12.2 allowed to fail manual
cross-ios universal examples
passed #599865
documentation

00:03:55