IPv6 route check: list devices only once
IPv6 route check: list devices only once

If several RA routes are found for the same device, only list that
device once in the error message.

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