[NETFILTER]: nf_conntrack: optimize hash_conntrack()

Avoid calling jhash three times and hash the entire tuple in one go.

  __hash_conntrack | -485 # 760 -> 275, # inlines: 3 -> 1, size inlines: 717 -> 252
 1 function changed, 485 bytes removed

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>