The new jhash implementation

The current jhash.h implements the lookup2() hash function by Bob Jenkins.
However, lookup2() is outdated as Bob wrote a new hash function called
lookup3(). The patch replaces the lookup2() implementation of the 'jhash*'
functions with that of lookup3().

You can read a longer comparison of the two and other hash functions at
http://burtleburtle.net/bob/hash/doobs.html.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>