ospfd: Add Segment Routing Local Block

ospfd: Add Segment Routing Local Block

RFC 8665 defines a Segment Routing Local Block for Adjacency SID.
This patch provides the possibility to modify the SRLB as well as
reserved the block range from the Label Manager.

 - Introduce new CLI 'segment-routing local-block'
 - Add local block to SRDB structure
 - Parse / Serialize SRLB in Router Information LSA
 - Update OSPF-SR topotest
 - Update documentation

Signed-off-by: Olivier Dugeon <olivier.dugeon@orange.com>