ipv6: fix backtracking for throw routes

for throw routes to trigger evaluation of other policy rules
EAGAIN needs to be propagated up to fib_rules_lookup
similar to how its done for IPv4

A simple testcase for verification is:

ip -6 rule add lookup 33333 priority 33333
ip -6 route add throw 2001:db8::1
ip -6 route add 2001:db8::1 via fe80::1 dev wlan0 table 33333
ip route get 2001:db8::1
Signed-off-by: Steven Barth <cyrus@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/fib6_rules.c

@@ -104,6 +104,7 @@ static int fib6_rule_action(struct fib_rule *rule, struct flowi *flp,
 				goto again;
 			flp6->saddr = saddr;
 		}
+		err = rt->dst.error;
 		goto out;
 	}
 again: