Activate Segment Routing by default

Activate Segment Routing by default

Since Aluminium release, Segment Routing was wrongly disabled by
default, following the commit that update SR to latest RFC.

In previous release it was activated by default and the documentation
let users thinks it was enabled by default. This commit revert the
previous behavior.

JIRA: BGPCEP-972
Change-Id: Ia8c36e43e026dc576a6ef7b0f2faeac1bc9bef65
Signed-off-by: Olivier Dugeon <olivier.dugeon@orange.com>
(cherry picked from commit 9017e70427626d244a10d4aaf4661cca4bd4d1e8)