[Multi-asic] Fixed Default Route to be BGP (#5548)

Learned and not docker default route for multi-asic platforms.

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>

dockers/docker-fpm-frr/start.sh

@@ -4,27 +4,34 @@ mkdir -p /etc/frr
 
 CONFIG_TYPE=`sonic-cfggen -d -v 'DEVICE_METADATA["localhost"]["docker_routing_config_mode"]'`
 
-if [[ ! -z "$NAMESPACE_ID" ]]; then
+update_default_gw()
+{
+   IP_VER=${1}
    # FRR is not running in host namespace so we need to delete
    # default gw kernel route added by docker network via eth0 and add it back
    # with higher administrative distance so that default route learnt
    # by FRR becomes best route if/when available
-   GATEWAY_IP=$(ip route show 0.0.0.0/0 dev eth0 | awk '{print $3}')
+   GATEWAY_IP=$(ip -${IP_VER} route show default dev eth0 | awk '{print $3}')
    #Check if docker default route is there
    if [[ ! -z "$GATEWAY_IP" ]]; then
-      ip route del 0.0.0.0/0 dev eth0
+      ip -${IP_VER} route del default dev eth0
       #Make sure route is deleted
-      CHECK_GATEWAY_IP=$(ip route show 0.0.0.0/0 dev eth0 | awk '{print $3}')
+      CHECK_GATEWAY_IP=$(ip -${IP_VER} route show default dev eth0 | awk '{print $3}')
       if [[ -z "$CHECK_GATEWAY_IP" ]]; then
          # Ref: http://docs.frrouting.org/en/latest/zebra.html#zebra-vrf
          # Zebra does treat Kernel routes as special case for the purposes of Admin Distance. \
          # Upon learning about a route that is not originated by FRR we read the metric value as a uint32_t.
          # The top byte of the value is interpreted as the Administrative Distance and
          # the low three bytes are read in as the metric.
          # so here we are programming administrative distance of 210 (210 << 24) > 200 (for routes learnt via IBGP)
-         ip route add 0.0.0.0/0 via $GATEWAY_IP dev eth0 metric 3523215360
+         ip -${IP_VER} route add default via $GATEWAY_IP dev eth0 metric 3523215360
       fi
    fi
+}
+
+if [[ ! -z "$NAMESPACE_ID" ]]; then
+   update_default_gw 4
+   update_default_gw 6
 fi
 
 if [ -z "$CONFIG_TYPE" ] || [ "$CONFIG_TYPE" == "separated" ]; then