[IPVS]: Switch to using ctl_paths.

The feature of ipvs ctls is that the net/ipv4/vs path
is common for core ipvs ctls and for two schedulers,
so I make it exported and re-use it in modules.

Two other .c files required linux/sysctl.h to make the
extern declaration of this path compile well.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>