net ipv6: Don't use sysctl tables with .child entries.

The sysctl core no longer natively understands sysctl tables
with .child entries.

Split the ipv6_table to remove the .child entries.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>