common/mlx5: optimize cache list object memory

common/mlx5: optimize cache list object memory

Currently, hash list uses the cache list as bucket list. The list
in the buckets have the same name, ctx and callbacks. This wastes
the memory.

This commit abstracts all the name, ctx and callback members in the
list to a constant struct and others to the inconstant struct, uses
the wrapper functions to satisfy both hash list and cache list can
set the list constant and inconstant struct individually.

Signed-off-by: Suanming Mou <suanmingm@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>