Make normalized cache path larger

On larger instances with a large number of shares this can make a real
impact as the default 512 entries are easily filled.

Making this contain max 2048 entries has basically no effect on smaller
installations (as they probably never hit the 512 now). But makes sure
we don't evict entries in the larger case.

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>