tests/mpool: lower minimum bound for mpool vs. malloc

This is needed for FreeBSD 14.0 with clang; evidently, they improved the
malloc speed.  (The previous limits were still fine for freebsd 14.0
with gcc.)

tests/mpool/test_mpool.sh

@@ -116,14 +116,14 @@ printf "sets\treps\tratio\n"
 
 # Test with full benefit from malloc pool (the binary begins with an
 # initial pool of 100).
-cmp_methods 10000 100 200 "full"
+cmp_methods 10000 100 180 "full"
 
 # mpool is still considerably faster than malloc in this range.
 cmp_methods 1000 1000 200 "partial"
 
 # mpool is not much slower than malloc even when there's no benefit
 # from the pool.
-cmp_methods 1 1000000 90 "none"
+cmp_methods 1 1000000 85 "none"
 
 # Test again with valgrind (if enabled).
 if [ -n "${c_valgrind_cmd}" ]; then