Allow both LNTF to coexist with NACKs and key frame requests
Allow both LNTF to coexist with NACKs and key frame requests

LNTF (loss notifications) are no longer mutually exclusive with
NACK and key frames; a receiver may send both, and the sender would
be allowed to choose which to regard.

Bug: webrtc:10336
Change-Id: I1ae7d972f9f47b07fe2f493bb31c1916456d6a3a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/138828
Reviewed-by: Ilya Nikolaevskiy <76788ac3efd229e9d156135d9ceb7fef65c45da4@webrtc.org>
Commit-Queue: Elad Alon <9d66cb9c3c57b29e6fc055a4405dac15e20e28ee@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28081}

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