hash: rename unused field

hash: rename unused field

The cuckoo hash has a fixed number of entries per bucket, so the
configuration parameter for this is unused. We change this field in the
parameters struct to "reserved" to indicate that there is now no such
parameter value, while at the same time keeping ABI consistency.

Fixes: 48a399119619 ("hash: replace with cuckoo hash implementation")

Suggested-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>