SELinux: calculate and print hashtab stats with a generic function

We have custom debug functions like rangetr_hash_eval and symtab_hash_eval
which do the same thing.  Just create a generic function that takes the name
of the hash table as an argument instead of having custom functions.

Signed-off-by: Eric Paris <eparis@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>