netns: Add network namespace argument to rt6_fill_node() and ipv6_dev_get_saddr()

ipv6_dev_get_saddr() blindly de-references dst_dev to get the network
namespace, but some callers might pass NULL.  Change callers to pass a
namespace pointer instead.

Signed-off-by: Brian Haley <brian.haley@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_fib.c

@@ -378,6 +378,7 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
 
 	arg.skb = skb;
 	arg.cb = cb;
+	arg.net = net;
 	w->args = &arg;
 
 	for (h = s_h; h < FIB_TABLE_HASHSZ; h++, s_e = 0) {