IPVS: Allow configuration of persistence engines

Allow the persistence engine of a virtual service to be set, edited
and unset.

This feature only works with the netlink user-space interface.

Signed-off-by: Simon Horman <horms@verge.net.au>
Acked-by: Julian Anastasov <ja@ssi.bg>

include/linux/ip_vs.h

@@ -336,6 +336,9 @@ enum {
 	IPVS_SVC_ATTR_NETMASK,		/* persistent netmask */
 
 	IPVS_SVC_ATTR_STATS,		/* nested attribute for service stats */
+
+	IPVS_SVC_ATTR_PE_NAME,		/* name of ct retriever */
+
 	__IPVS_SVC_ATTR_MAX,
 };