ipvs: Move userspace definitions to include/linux/ip_vs.h

Current versions of ipvsadm include "/usr/src/linux/include/net/ip_vs.h"
directly. This file also contains kernel-only definitions. Normally, public
definitions should live in include/linux, so this patch moves the
definitions shared with userspace to a new file, "include/linux/ip_vs.h".

This also removes the unused NFC_IPVS_PROPERTY bitmask, which was once
used to point into skb->nfcache.

To make old ipvsadms still compile with this, the old header file includes
the new one.

Thanks to Dave Miller and Horms for noting/adding the missing Kbuild entry
for the new header file.

Signed-off-by: Julius Volz <juliusv@google.com>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>