Factor out access to `Call::receive_rtp_config_`

This CL adds a SequenceChecker, receive_11993_checker_, specifically for
variables that need to move to the network thread. Once migrated,
the checker will be replaced with a check for the network thread.

In the meantime, the checker will match with one of worker [x]or
network threads.

As a first step, this checker is used to isolate access to
`receive_rtp_config_` which is used from object factory paths (Create/
Destroy routines) as well as paths that handle network packets.

Bug: webrtc:11993
Change-Id: Ia58423583cf99492018f218eb1640535e3919193
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/249080
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35800}