fix: fip unbind can't take effect immediately when conntrack record exists (#1922)

dist/images/vpcnatgateway/Dockerfile

@@ -8,7 +8,8 @@ RUN set -ex \
     iproute2 \
     iptables \
     iputils \
-    tcpdump
+    tcpdump \
+    conntrack-tools
 
 WORKDIR /kube-ovn
 COPY nat-gateway.sh /kube-ovn/

dist/images/vpcnatgateway/nat-gateway.sh

@@ -159,6 +159,7 @@ function del_floating_ip() {
         if [ "$?" -eq 0 ];then
             exec_cmd "iptables -t nat -D EXCLUSIVE_DNAT -d $eip -j DNAT --to-destination $internalIp"
             exec_cmd "iptables -t nat -D EXCLUSIVE_SNAT -s $internalIp -j SNAT --to-source $eip"
+            exec_cmd "conntrack -D -d $eip"
         fi
     done
 }