net: if: Remove local address from IPv6 neighbor cache

When we do DAD (Duplicate Address Detection), the local IPv6
address gets added to the neighbor cache. This is useless so
remove it after DAD has finished.

Change-Id: I9625d367e96d8108a7d3d1d8b2e95f3c4ea11c45
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>