ospf: T5377: add graceful restart FRR feature (RFC 3623)

New CLI commands:

• set protocols ospf graceful-restart grace-period 300
• set protocols ospf graceful-restart helper planned-only
• set protocols ospf graceful-restart helper no-strict-lsa-checking
• set protocols ospf graceful-restart helper supported-grace-time 400
• set protocols ospf graceful-restart helper enable router-id 192.0.2.1
• set protocols ospf graceful-restart helper enable router-id 192.0.2.2

• set protocols ospfv3 graceful-restart grace-period 300
• set protocols ospfv3 graceful-restart helper planned-only
• set protocols ospfv3 graceful-restart helper lsa-check-disable
• set protocols ospfv3 graceful-restart helper supported-grace-time 400
• set protocols ospfv3 graceful-restart helper enable router-id 192.0.2.1
• set protocols ospfv3 graceful-restart helper enable router-id 192.0.2.2