iputils: fix various arping regressions

arping in iputils s20190709 has several problems, this backports the
fixes from s20200821.
 - -D, duplicate address detection, always returns failure
 - -w -f does not behave correctly
 - -w option hangs arping
 - -U option returns failure

Signed-off-by: Diego Santa Cruz <Diego.SantaCruz@spinetix.com>