SKYH4-5190: Misleading value for "Delegated Prefix" attribute on GUI.
SKYH4-5190: Misleading value for "Delegated Prefix" attribute on GUI.

Reason for change: "Device.IP.Interface.1.IPv6Prefix.1.Prefix" data model value is from the
"tr_erouter0_dhcpv6_client_v6pref" sysevent. Currently, is set to "/64" in the
WAN manager and PAM component.
Changing the sysevent to the received wan prefix to show correct results in the webUI.

Test Procedure:
1. Checked zebra process and its configurations.
2. Checked dibbler server process and its confirations.

Risks: Low

Signed-off-by: Abhishek Sivappa <7e3eb8981bec8c18a3ba1b7080ab5e6852298347@sky.uk>
(cherry picked from commit 86cfb34cce28c6e1fd3b87ca612b8ba7b5281e02)
Change-Id: I672c4bedce01c29cdfb7667583d312068591e392

rdkcmf/rdkb-CcspPandM,rdkcmf/rdkb-CcspPandM,rdkcmf/rdkb-CcspPandM