Optimize attach endpoint for repetitive ADD calls

[ashvindeodhar]

Is this a request for help?:

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Is this an ISSUE or FEATURE REQUEST? (choose one):
Optimization

Which release version?:
v1.0.22

Which component (CNI/IPAM/CNM/CNS):
CNI

Which Operating System (Linux/Windows):
Windows

For Linux: Include Distro and kernel version using "uname -a"

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For windows: provide output of "$(Get-ItemProperty -Path "C:\windows\system32\hal.dll").VersionInfo.FileVersion"
10.0.17763.529 (WinBuild.160101.0800)

Which Orchestrator and version (e.g. Kubernetes, Docker)
k8s

What happened:
For the repetitive CNI ADD calls for the same pause container, azure CNI will try to invoke HNS and attach the endpoint to the container again. consecutiveAdd is not needed for the pause container ADD.

What you expected to happen:
Azure CNI can optimize this by not invoking HNS and returning early.

How to reproduce it (as minimally and precisely as possible):
Create container on windows.

Anything else we need to know:

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