param: Restore old default h2_max_header_list_size

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.

include/tbl/params.h

@@ -1288,7 +1288,7 @@ PARAM_SIMPLE(
 	/* name */	h2_max_header_list_size,
 	/* type */	bytes_u,
 	/* min */	"0b",
-	/* max */	"4294967295b",
+	/* max */	"2147483647b", /* NB: not the RFC maximum */
 	/* def */	"0b",
 	/* units */	"bytes",
 	/* descr */