Except that the old default value replaces the maximum one. Aligning
with the literal maximum value for the underlying HTTP/2 setting breaks
32bit builds because the byte tweaks take a detour via ssize_t. When it
casts to uintmax_t the MSB is propagated all the way, triggering the
following error at build time:

> 4294967295b is too large for this architecture.

Instead of fighting a tweak that is clearly wrong, grant h2 clients a
maximum of 2GB of uncompressed headers (instead of 4GB) that will never
happen, because h2 is overall much wronger.