hash: move struct field to keep ABI stable

hash: move struct field to keep ABI stable

In order to keep the ABI consistent with the old hash library,
hash_func_init_val field has been moved, so it remains
at the same offset as previously, since hash_func and
hash_func_init_val are fields accessed by the public function
rte_hash_hash and must keep the same offset as older versions.

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

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>