Flush remaining routes from the routing table during VNET shutdown.

Summary:
This fixes rtentry leak for the cloned interfaces created inside the
 VNET.

PR:	253998
Reported by:	rashey at superbox.pl
MFC after:	3 days

Loopback teardown order is `SI_SUB_INIT_IF`, which happens after `SI_SUB_PROTO_DOMAIN` (route table teardown).
Thus, any route table operations are too late to schedule.
As the intent of the vnet teardown procedures to minimise the amount of effort by doing global cleanups instead of per-interface ones, address this by adding a relatively light-weight routing table cleanup function, `rib_flush_routes()`.
It removes all remaining routes from the routing table and schedules the deletion, which will happen later, when `rtables_destroy()` waits for the current epoch to finish.

Test Plan:
```
set_skip:set_skip_group_lo  ->  passed  [0.053s]
tail -n 200 /var/log/messages | grep rtentry
```

Reviewers: #network, kp, bz

Reviewed By: kp

Subscribers: imp, ae

Differential Revision: https://reviews.freebsd.org/D29116

sys/net/route.c

@@ -493,21 +493,6 @@ rt_ifdelroute(const struct rtentry *rt, const struct nhop_object *nh, void *arg)
 	return (1);
 }
 
-/*
- * Delete all remaining routes using this interface
- * Unfortuneatly the only way to do this is to slog through
- * the entire routing table looking for routes which point
- * to this interface...oh well...
- */
-void
-rt_flushifroutes_af(struct ifnet *ifp, int af)
-{
-	KASSERT((af >= 1 && af <= AF_MAX), ("%s: af %d not >= 1 and <= %d",
-	    __func__, af, AF_MAX));
-
-	rib_foreach_table_walk_del(af, rt_ifdelroute, ifp);
-}
-
 void
 rt_flushifroutes(struct ifnet *ifp)
 {

sys/net/route.h

@@ -429,7 +429,6 @@ struct sockaddr *rtsock_fix_netmask(const struct sockaddr *dst,
 
 void	rt_updatemtu(struct ifnet *);
 
-void	rt_flushifroutes_af(struct ifnet *, int);
 void	rt_flushifroutes(struct ifnet *ifp);
 
 /* XXX MRT NEW VERSIONS THAT USE FIBs
@@ -442,6 +441,7 @@ int	rib_lookup_info(uint32_t, const struct sockaddr *, uint32_t, uint32_t,
 void	rib_free_info(struct rt_addrinfo *info);
 
 /* New API */
+void rib_flush_routes_family(int family);
 struct nhop_object *rib_lookup(uint32_t fibnum, const struct sockaddr *dst,
 	    uint32_t flags, uint32_t flowid);
 #endif

sys/net/route/route_ctl.c

@@ -1328,6 +1328,42 @@ rib_walk_del(u_int fibnum, int family, rib_filter_f_t *filter_f, void *arg, bool
 	NET_EPOCH_EXIT(et);
 }
 
+static int
+rt_delete_unconditional(struct radix_node *rn, void *arg)
+{
+	struct rtentry *rt = RNTORT(rn);
+	struct rib_head *rnh = (struct rib_head *)arg;
+
+	rn = rnh->rnh_deladdr(rt_key(rt), rt_mask(rt), &rnh->head);
+	if (RNTORT(rn) == rt)
+		rtfree(rt);
+
+	return (0);
+}
+
+/*
+ * Removes all routes from the routing table without executing notifications.
+ * rtentres will be removed after the end of a current epoch.
+ */
+static void
+rib_flush_routes(struct rib_head *rnh)
+{
+	RIB_WLOCK(rnh);
+	rnh->rnh_walktree(&rnh->head, rt_delete_unconditional, rnh);
+	RIB_WUNLOCK(rnh);
+}
+
+void
+rib_flush_routes_family(int family)
+{
+	struct rib_head *rnh;
+
+	for (uint32_t fibnum = 0; fibnum < rt_numfibs; fibnum++) {
+		if ((rnh = rt_tables_get_rnh(fibnum, family)) != NULL)
+			rib_flush_routes(rnh);
+	}
+}
+
 static void
 rib_notify(struct rib_head *rnh, enum rib_subscription_type type,
     struct rib_cmd_info *rc)

sys/netinet/ip_input.c

@@ -379,7 +379,6 @@ ip_init(void)
 static void
 ip_destroy(void *unused __unused)
 {
-	struct ifnet *ifp;
 	int error;
 
 #ifdef	RSS
@@ -405,10 +404,7 @@ ip_destroy(void *unused __unused)
 	in_ifscrub_all();
 
 	/* Make sure the IPv4 routes are gone as well. */
-	IFNET_RLOCK();
-	CK_STAILQ_FOREACH(ifp, &V_ifnet, if_link)
-		rt_flushifroutes_af(ifp, AF_INET);
-	IFNET_RUNLOCK();
+	rib_flush_routes_family(AF_INET);
 
 	/* Destroy IP reassembly queue. */
 	ipreass_destroy();

sys/netinet6/ip6_input.c

@@ -386,11 +386,12 @@ ip6_destroy(void *unused __unused)
 		/* IF_ADDR_UNLOCK(ifp); */
 		in6_ifdetach_destroy(ifp);
 		mld_domifdetach(ifp);
-		/* Make sure any routes are gone as well. */
-		rt_flushifroutes_af(ifp, AF_INET6);
 	}
 	IFNET_RUNLOCK();
 
+	/* Make sure any routes are gone as well. */
+	rib_flush_routes_family(AF_INET6);
+
 	frag6_destroy();
 	nd6_destroy();
 	in6_ifattach_destroy();