Call verification of upgrade and channel before start flush in ack handler

[colin-axner]

Summary

startFlushUpgradeHandshake will be remade to be a write function. In order to do this we will pull out the verify functions. We will start by adding duplicate verify funcs and then remove the verify funcs from start flush when they are no longer needed.

Add the same verification done here to the upgrade ack handler here

A followup issue will be opened to create a helper function for the upgrade verification

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