Rename ifaceMacvtapLinkAdd to virNetDevMacVLanCreate and
ifaceLinkDel to virNetDevMacVLanDelete. Strictly speaking
the latter isn't restricted to macvlan devices, but that's
the only use libvirt has for it.

* util/interface.c, util/interface.h,
  util/virnetdevmacvlan.c: Rename APIs