Rename ifaceGetIndex and ifaceGetVLAN

Rename ifaceGetIndex and ifaceGetVLAN

Rename the ifaceGetIndex method to virNetDevGetIndex and
ifaceGetVlanID to virNetDevGetVLanID. Also change the error
reporting behaviour to always raise errors and return -1 on
failure

* util/interface.c, util/interface.h: Rename ifaceGetIndex
  and ifaceGetVLAN
* nwfilter/nwfilter_gentech_driver.c, nwfilter/nwfilter_learnipaddr.c,
  nwfilter/nwfilter_learnipaddr.c, util/virnetdevvportprofile.c: Update
  for API renames and error handling changes