Add BIRD OSPF graceful restart support

[jbemmel]

Summary

• Render BIRD OSPF graceful restart settings from ospf.gr.restart and ospf.gr.helper
• Declare IPv4/IPv6 OSPF GR capability for the bird daemon
• Document BIRD in the OSPF graceful restart platform table

Test plan

• netlab create on a topology with device: bird and ospf.gr.restart / ospf.gr.helper
• Verify generated ospf.mod.conf contains graceful restart on or graceful restart aware
• Confirm ospf.gr validation passes for bird nodes with IPv4 and IPv6

Made with Cursor

[jbemmel]

BIRD establishes the adjacency quickly, but the GR helper seems to need a few moments more:

netlab connect dut birdcl

show protocols
debug ospf_global_v3 { states,routes,events }
echo all

Added a 5-second extra wait for BIRD only, which stabilizes the test. Tried to find a more explicit state to watch for, but no luck

Also improved the GR reset logic at the end, to enable repeated GR tests