net: route: convert routing statistics to a sysctl

Exporting the relevant pcpustat is trivial, so let's do that.  We will
use it in a near-future change in netstat to avoid having to dig around
in mem(4) for live kernel statistics.

Differential Revision:	https://reviews.freebsd.org/D47231

sys/net/route.c

@@ -75,6 +75,10 @@ VNET_PCPUSTAT_SYSINIT(rtstat);
 VNET_PCPUSTAT_SYSUNINIT(rtstat);
 #endif
 
+SYSCTL_DECL(_net_route);
+SYSCTL_VNET_PCPUSTAT(_net_route, OID_AUTO, stats, struct rtstat,
+    rtstat, "route statistics");
+
 EVENTHANDLER_LIST_DEFINE(rt_addrmsg);
 
 static int rt_ifdelroute(const struct rtentry *rt, const struct nhop_object *,

sys/net/route.h

@@ -239,6 +239,7 @@ struct rtstat {
 	uint64_t rts_add_retry;		/* # of route addition retries */
 	uint64_t rts_del_failure;	/* # of route deletion failure */
 	uint64_t rts_del_retry;		/* # of route deletion retries */
+	uint64_t rts_spare[5];
 };
 
 /*