Create rate allocator after codec bitrates are set.
Create rate allocator after codec bitrates are set.

Before this change the max bitrate could be updated after it was passed
to rate allocator.

Bug: none
Change-Id: I742fca0f122bef3e95c1a768d6e844f8c28b6279
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/141661
Reviewed-by: Erik Språng <3ab8c90c99d6dd7822e0fad803ab0211dd287ae5@webrtc.org>
Commit-Queue: Sergey Silkin <fc631354f276613a5410ea259cf4618b2846d39b@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28253}

TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc