Sleep done before mismatch handler (#4165)

* Sleep done before mismatch handler

files/scripts/arp_update

@@ -47,6 +47,9 @@ while /bin/true; do
       eval `eval $ip6cmd`
   done
 
+  # sleep here before handling the mismatch as it is not required during startup
+  sleep 300
+
   # refresh neighbor entries from APP_DB in case of mismatch with kernel
   DBNEIGH=$(sonic-db-cli APPL_DB keys NEIGH_TABLE*)
   KERNEIGH4=$(ip -4 neigh show | grep Vlan | cut -d ' ' -f 1,3  --output-delimiter=',')
@@ -67,5 +70,4 @@ while /bin/true; do
       fi
   done
 
-  sleep 300
 done