rtpulpfecenc: Create a FEC packet for the last N packets in non-mp mode

One still needs to accumulate packets when not in multi-packet mode, the
FEC packet will still protect the last "x" packets even if they are unrelated.
8 jobs for fecenc-non-multipacket in 38 minutes and 29 seconds (queued for 31 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #183974
gst indent

00:00:37

passed #183973
manifest

00:00:29

 
  Build
passed #183975
build fedora x86_64

00:07:16

 
  Test
passed #183976
check fedora

00:04:41

 
  Full Builds
passed #183978
build cerbero android universal

00:21:23

passed #183979
build cerbero cross win32

00:09:58

passed #183980
build cerbero cross win64

00:06:53

passed #183977
build cerbero fedora x86_64

00:10:40