The src/lxc/veth.c file contains APIs for managing veth devices,
but some of the APIs duplicate stuff from src/util/virnetdev.h.
Delete thed duplicate APIs and rename the remaining ones to
follow virNetDevVethXXXX

* src/lxc/veth.c, src/lxc/veth.h: Rename APIs & delete duplicates
* src/lxc/lxc_container.c, src/lxc/lxc_controller.c,
  src/lxc/lxc_driver.c: Update for API renaming