ip-lib : "ip neigh" command should use "replace" instead of "add"

[Mathieu Rohon]

with l2-population and linuxbridge agent, we used to use "ip neigh" command to add arp responder entries :
this command has been generalized with this patch :
https://review.openstack.org/#/c/88442/3

but using "ip neigh add" leads to a bug when restoring a previous entry :
https://bugs.launchpad.net/neutron/+bug/1282662

we should use "ip neigh replace" instead of "ip neigh add'"

[Openstack Gerrit (openstack-gerrit)]

Fix proposed to branch: master
Review: https://review.openstack.org/89522

[Openstack Gerrit (openstack-gerrit)]

Reviewed: https://review.openstack.org/89522
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=6ca8e28d3100b1860af5f36d7a0e59fc7b500c29
Submitter: Jenkins
Branch: master

commit 6ca8e28d3100b1860af5f36d7a0e59fc7b500c29
Author: mathieu-rohon <email address hidden>
Date: Tue Apr 22 11:44:35 2014 +0200

    ip-lib : use "ip neigh replace" instead of "ip neigh add"

    Closes bug #1311002

    Change-Id: Ie50bc0bff32b7f97ac317ccc2521bbea52d59ca3