IPVS: Add persistence engine data to /proc/net/ip_vs_conn

This shouldn't break compatibility with userspace as the new data
is at the end of the line.

I have confirmed that this doesn't break ipvsadm, the main (only?)
user-space user of this data.

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

include/net/ip_vs.h

@@ -572,6 +572,7 @@ struct ip_vs_pe {
 			 struct ip_vs_conn *ct);
 	u32 (*hashkey_raw)(const struct ip_vs_conn_param *p, u32 initval,
 			   bool inverse);
+	int (*show_pe_data)(const struct ip_vs_conn *cp, char *buf);
 };
 
 /*