sunrpc: increase MAX_HASHTABLE_BITS to 14

The maximum size of the authcache is now set to 1024 (10 bits),
but on our server we need at least 4096 (12 bits). Increase
MAX_HASHTABLE_BITS to 14. This is a maximum of 16384 entries,
each containing a pointer (8 bytes on x86_64). This is
exactly the limit of kmalloc() (128K).

Signed-off-by: Miquel van Smoorenburg <mikevs@xs4all.net>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>