tomoyo: improve hash bucket dispersion

When examining the network device name hash, it was discovered that
the low order bits of full_name_hash() are not very well dispersed
across the possible values. When used by filesystem code, this is handled
by folding with the function hash_long().

The only other non-filesystem usage of full_name_hash() at this time
appears to be in TOMOYO. This patch should fix that.

I do not use TOMOYO at this time, so this patch is build tested only.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>