Comment 9 for bug 1724595

Reviewed: https://review.opencontrail.org/35131
Committed: http://github.com/Juniper/contrail-controller/commit/554a31d8fe15239b7f9536ab73f5ddcf8fb8ecba
Submitter: Zuul (<email address hidden>)
Branch: master

commit 554a31d8fe15239b7f9536ab73f5ddcf8fb8ecba
Author: Andrey Shestakov <email address hidden>
Date: Tue Aug 29 14:57:48 2017 +0300

Set DHCP siaddr to IP of the TFTP server if set

DHCP clarifies the interpretation of the 'siaddr' field as the
address of the server to use in the next step of the client's
bootstrap process according to rfc 2131
https://www.ietf.org/rfc/rfc2131.txt

TSN node doesn't provide tftp service, and for baremetal provisioning
the tftp is located on ironic-conductor host.

This patch update DHCP to set siaddr to value set in option 66 if
provided.

Closes-Bug: #1724595

Change-Id: I997585ffacbeb0fd86b95a3489abd832f1b391d9