core_namemap.c: 2048 hashtable buckets should be sufficient

core_namemap.c: 2048 hashtable buckets should be sufficient

It is unlikely we would need more than 4000 names and even
with more names (up to 8192) it would still work, just
the performance fo the namemap would degrade.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/24504)