net: Move free of dst_metrics to helper

Move the refcounting and potential free of dst metrics associated
for ipv4 and ipv6 to a common helper.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ip.h b/include/net/ip.h
index f9a7125..72593e1 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -441,6 +441,15 @@ void ip_dst_init_metrics(struct dst_entry *dst, struct dst_metrics *fib_metrics)
 	}
 }
 
+static inline
+void ip_dst_metrics_put(struct dst_entry *dst)
+{
+	struct dst_metrics *p = (struct dst_metrics *)DST_METRICS_PTR(dst);
+
+	if (p != &dst_default_metrics && refcount_dec_and_test(&p->refcnt))
+		kfree(p);
+}
+
 u32 ip_idents_reserve(u32 hash, int segs);
 void __ip_select_ident(struct net *net, struct iphdr *iph, int segs);