pimd, zebra: request for replay of SG entries on startup

pimd, zebra: request for replay of SG entries on startup

zvni setup in zebra is controlled via bgpd i.e. advertise_all_vni
from bgpd triggers this setup. As a part of zvni creation we may need
to setup BUM mcast SG entries which are propagated to pimd for MDT setup.

Now pimd may not be present at the time of zvni creation or may restart
post zvni creation so we need a mechanism to replay (on pimd startup) and
to cleanup (on pimd stop). This is addressed via zebra_vxlan_sg_replay and
zebra_evpn_pim_cfg_clean_up.

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>