systemvm: vpc router fix /etc/network/interfaces is misconfigured (#6435)

This PR fixes that the /etc/network/interfaces is misconfigured in VPC VR startup, which causes VPC VR to be stuck for 1 minute and continue working.

The issue is because ifup eth0 and ifdown eth0 do not work when /etc/network/interfaces is not correct in VPC VR.

systemvm/debian/opt/cloud/bin/setup/init.sh

@@ -188,6 +188,7 @@ setup_interface_sshd() {
     setup_sshd $ETH1_IP "eth1"
 
   elif [ "$TYPE" == "vpcrouter" ]; then
+    init_interfaces "eth0"
     setup_interface "0" $ETH0_IP $ETH0_MASK $GW
     setup_sshd $ETH0_IP "eth0"
 

systemvm/debian/opt/cloud/bin/setup/vpcrouter.sh

@@ -25,11 +25,6 @@ setup_vpcrouter() {
     grep -q $NAME /etc/hosts || echo "127.0.0.1 $NAME" >> /etc/hosts;
   fi
 
-    cat > /etc/network/interfaces << EOF
-auto lo eth0
-iface lo inet loopback
-EOF
-
   echo $NAME > /etc/hostname
   echo 'AVAHI_DAEMON_DETECT_LOCAL=0' > /etc/default/avahi-daemon
   hostnamectl set-hostname $NAME