libvirt-domain: Document interface stats POV
libvirt-domain: Document interface stats POV

Interestingly enough, we don't document the point of view of the
interface statistics. Therefore it's unknown to users if for
instance rx_packets is the number of packets received by domain or
received by host (from domain). Document this explicitly.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

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