[balsa] Process request trailers. (#22240)
[balsa] Process request trailers. (#22240)

Call framer_.set_balsa_trailer() not only for responses but also for
requests.  Support for this has been added to Balsa recently at
https://github.com/google/quiche/commit/4fddcf2647c4f9f5a397dc3d6d1bc790ca977a82

Signed-off-by: Bence Béky <4815a8677a9803667dd9fb123cefbce31fbbc718@google.com>
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