Original PR: #9331

RELEASE NOTES:
* transport: restrict memory overhead of buffering small data frames.

Original PRs: #9258 and #9332

RELEASE NOTES:
- xds/rbac: Fix a bug where nested `Principal` or `Permission` rules
with `:scheme` or `grpc-` prefixed header matchers were not rejected,
which could cause DENY rules to fail open.
- xds/rbac: Fix a bug where the `host` header matcher was not being
replaced with `:authority` in nested `Principal` or `Permission` rules.
- xds/rbac: Fix a bug where a header matcher whose name was not
lowercase, such as `X-Role`, matched no header, which could cause DENY
rules to fail open.
- xds/rbac: Fix a bug where a `:scheme` or `grpc-` prefixed header
matcher was accepted when its name was not lowercase.
- xds/rbac: Fix a bug where a `Host` header matcher was not replaced
with `:authority`.

---------

Co-authored-by: Naveed <naveed@bugqore.com>
Co-authored-by: Markus Magnuson <331091+alimony@users.noreply.github.com>

RELEASE NOTES: None