Tweak IAP transport to only delay control sessions, not data sessions

[joeljfischer]

Fixes #1240

This PR is ready for review.

Risk

This PR makes no API changes.

Testing Plan

Smoke tests were performed with the following scenarios:

1. 6 apps were forced to connect with this branch on the control protocol repeatedly.
2. 13 apps were forced to connect with this branch on the multisession protocol repeatedly.

Summary

This PR updates the IAP transport to only delay apps from connecting with their retry delay when the control session is being used for connection, not when the multisession protocol (direct to data session) is being used.

Changelog

Bug Fixes

• Connecting to newer head units using the multisession protocol is sped up.

CLA

• I have signed the CLA

[NicoleYarroch]

There are some issues with changing the head unit language:

1. If the SDL app is connected to the head unit when the user changes the head unit language, the ChangeRegistration fails most of the time due VR not being ready (I consider this to be an edge case).
2. The session often fails to close correctly when switching the head unit language while the SDL app is connected. I tested closing the session if the I/O thread in the data session does not close in the sdl_accessoryEventLoop and it seemed to fix the issue: https://gist.github.com/NicoleYarroch/1861152ac88f07e59fba9ca5b4173f6c

[NicoleYarroch]

Left a comment about some issues.

[joeljfischer]

I added your suggested fix for (2). I'm not seeing an issue with (1) here.