Merge pull request #8767 from opensourcerouting/ospfd-gr

ospfd: introduce support for Graceful Restart (restarting mode)

diff --cc configure.ac
Simple merge

diff --cc ospfd/ospf_flood.c
Simple merge

diff --cc ospfd/ospf_lsa.c
Simple merge

diff --cc ospfd/ospf_vty.c
Simple merge

diff --cc ospfd/ospf_zebra.c
Simple merge

diff --cc tests/topotests/lib/common_config.py
Simple merge