Fix#7968
Issue is detected on SONiC.20201231.11
In test_static_route.py::test_static_route_ecmp static routes are configured, but neighbors are not resolved after config reload even after 10 minutes.
It looks like the arp_update script is starting to ping when Vlan1000 is not fully configured.
When issue is reproduced, stuck ping6 process is observed in swss container :
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 180 0.1 0.0 6296 1272 pts/0 S 17:03 0:03 ping6 -I Vlan1000 -n -q -i 0 -c 1 -W 0 ff02::1
And when arp_update script successfully resolves neighbors, we observe sleep 300 instead of ping process
80e0627acc