rtpulpfec: use __restrict when building with MSVC on Windows

Microsoft compiler doesn't support the C99 standard keyword, only their
own alias.
8 jobs for msvc-restrict in 29 minutes and 42 seconds (queued for 2 minutes and 57 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #128779
gst indent

00:00:34

passed #128778
manifest

00:00:42

 
  Build
passed #128780
build fedora x86_64

00:05:58

 
  Test
passed #128781
check fedora

00:03:53

 
  Full Builds
passed #128782
build android arm64 api28

00:02:42

passed #128784
build cerbero cross win32

00:09:08

passed #128785
build cerbero cross win64

00:06:41

passed #128783
build cerbero fedora x86_64

00:10:19