Fixes bug 1042046
Sending gratuitous ARPs when a external router or a floating
IP was added in order to facilitate HA.
I am using iputils-arping package to send ARP packets. You will need
to install iputils-arping on Ubuntu and iputils on Fedora/RHEL/CentOS.
Arping locates in /usr/bin/arping on Ubuntu and locates in /sbin/arping
on Fedora/RHEL/CentOS.
Change-Id: I125dbc57b90027dc5e99ff0a5d6877843a0b02a5