process: Allow virProcessPrLimit() to get current limit
process: Allow virProcessPrLimit() to get current limit

The prlimit() function allows both getting and setting limits for
a process; expose the same functionality in our wrapper.

Add the const modifier for new_limit, in accordance with the
prototype for prlimit().

jfehlig/libvirt,olafhering/libvirt,nertpinx/libvirt,jfehlig/libvirt,taget/libvirt,crobinso/libvirt,zippy2/libvirt,libvirt/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,zippy2/libvirt,olafhering/libvirt,eskultety/libvirt,datto/libvirt,fabianfreyer/libvirt,zippy2/libvirt,crobinso/libvirt,rlaager/libvirt,taget/libvirt,crobinso/libvirt,datto/libvirt,rlaager/libvirt,olafhering/libvirt,eskultety/libvirt,olafhering/libvirt,nertpinx/libvirt,libvirt/libvirt,eskultety/libvirt,datto/libvirt,eskultety/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,datto/libvirt,nertpinx/libvirt,jardasgit/libvirt,taget/libvirt,rlaager/libvirt,nertpinx/libvirt,taget/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,rlaager/libvirt,libvirt/libvirt,crobinso/libvirt,datto/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,nertpinx/libvirt,zippy2/libvirt,jfehlig/libvirt,andreabolognani/libvirt,jardasgit/libvirt,libvirt/libvirt,andreabolognani/libvirt,eskultety/libvirt,rlaager/libvirt,taget/libvirt