Fix: Add default route on delegatedNIC interface

[paulyufan2]

Reason for Change:

This PR is to fix one issue in swiftv2 Windows scenario:
When a pod is created, the default route is added on infra vnet:
root@swiftv2-pod-3:/# ip route
default via 10.244.2.1 dev eth0 metric 1
It leads to ping a VM IP in the same VNET that cannot work.

There are two issues::
1.CNS does not provide the default route to CNI;
2.CNI should only add the default route to secondary interface customer vnet; on Swiftv2 scenario, skipDefaultRoutes is set to true for infraNIC interface and false for a secondary interface; so if !info.skipDefaultRoutes, then add default route.

Add dummy default route and pass to CNI as a workaround;

After this fix after a pod creation is done, the route table shows:
root@swiftv2-pod-1:/# ip route
default via 10.241.0.1 dev eth1
10.241.0.0/16 dev eth1 proto kernel scope link src 10.241.0.55
10.244.0.0/16 dev eth0 proto kernel scope link src 10.244.1.103

Issue Fixed:

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• relevant PR labels added

Notes:

[paulyufan2]

/azp run Azure Container Networking PR

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[paulyufan2]

/azp run Azure Container Networking PR

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).