aws-lc: do not use large buffer

aws-lc: do not use large buffer

test_10_08, uploading larger files for a h2 proxy, sporadically fails
with a decrpytion error on received data in AWS-LC. The frequency can
be increased by simulated network receive blocks.

Not setting a 4 * TLS record sized buffer, leaving AWS-LC at its
default buffer size seems to mitigate this problem.

Closes #18434