hash: add extendable bucket feature

hash: add extendable bucket feature

In use cases that hash table capacity needs to be guaranteed,
the extendable bucket feature can be used to contain extra
keys in linked lists when conflict happens. This is similar
concept to the extendable bucket hash table in packet
framework.

This commit adds the extendable bucket feature. User can turn
it on or off through the extra flag field during table
creation time.

Extendable bucket table composes of buckets that can be
linked list to current main table. When extendable bucket
is enabled, the hash table load can always achieve 100%.
In other words, the table can always accommodate the same
number of keys as the specified table size. This provides
100% table capacity guarantee.

Although keys ending up in the ext buckets may have longer
look up time, they should be rare due to the cuckoo
algorithm.

Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
Acked-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>