tsmux: When selecting random PIDs, name the pads according to those PIDs

Some elements will make use of the automatically generated names to
create new pads in future muxer instances, for example splitmuxsink.

Previously we would've created a pad with a random pid that would become
"sink_0", and then on a new muxer instance a pad "sink_0" and tsmux
would've then failed because 0 is not a valid PID.

Part-of: <gstreamer/gst-plugins-bad!2358>
29 jobs for !2358 with backport-mr-2318-into-1.18-tsmux-pad-name-with-pid in 26 minutes and 2 seconds (queued for 4 seconds)
detached
Status Name Job ID Coverage
  Build Docker
passed alpine amd64 manifest builder docker #11255460

00:00:30

passed android docker #11255459

00:00:32

passed cerbero fedora amd64 docker #11255458

00:00:31

passed fedora amd64 docker #11255457

00:00:32

passed gst-indent amd64 docker #11255461

00:00:45

 
  Preparation
passed gst indent #11255463

00:00:15

passed manifest #11255462

00:00:20

 
  Build
passed build cerbero cross-android universal #11255472
gstreamer

00:07:22

passed build cerbero cross-ios universal #11255476
gst-ios-14.3

00:20:18

passed build cerbero cross win32 #11255473
gstreamer

00:06:15

passed build cerbero cross win64 #11255474
gstreamer

00:06:13

passed build cerbero fedora x86_64 #11255471
gstreamer

00:05:28

passed build cerbero macos x86_64 #11255475
gst-macos-11.1

00:12:02

passed build clang fedora x86_64 #11255467

00:04:17

manual build msys2 #11255470
docker windows 1809 allowed to fail manual
passed build nodebug fedora x86_64 #11255464

00:04:18

passed build static fedora x86_64 #11255465

00:03:50

passed build static nodebug fedora x86_64 #11255466

00:03:24

passed build vs2017 amd64 #11255468
docker windows 1809

00:09:19

passed build vs2017 x86 #11255469
docker windows 1809

00:09:10

 
  Test
passed check fedora #11255477
gstreamer

00:06:59

passed integration testsuites fedora 1/4 #11255478
gstreamer

00:08:00

passed integration testsuites fedora 2/4 #11255479
gstreamer

00:08:41

passed integration testsuites fedora 3/4 #11255480
gstreamer

00:07:38

passed integration testsuites fedora 4/4 #11255481
gstreamer

00:09:22

passed valgrind bad #11255482
gstreamer

00:07:04

 
  Integrate
passed cross-android universal examples #11255483

00:07:24

passed cross-ios universal examples #11255485
gst-ios-14.3

00:04:33

passed documentation #11255484

00:13:12