ipv6: initialize ip6_route sysctl vars in ip6_route_net_init()

This makes that ip6_route_net_init() does all of the route init code.
There used to be a race between ip6_route_net_init() and ip6_net_init()
and someone relying on the combined result was left out cold.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>