[PATCH 3/3]ipv6:fix the outgoing interface selection order in udpv6_sendmsg()

1.When no interface is specified in an IPV6_PKTINFO ancillary data
  item, the interface specified in an IPV6_PKTINFO sticky optionis 
  is used.

RFC3542:
6.7.  Summary of Outgoing Interface Selection

   This document and [RFC-3493] specify various methods that affect the
   selection of the packet's outgoing interface.  This subsection
   summarizes the ordering among those in order to ensure deterministic
   behavior.

   For a given outgoing packet on a given socket, the outgoing interface
   is determined in the following order:

   1. if an interface is specified in an IPV6_PKTINFO ancillary data
      item, the interface is used.

   2. otherwise, if an interface is specified in an IPV6_PKTINFO sticky
      option, the interface is used.

Signed-off-by: Yang Hongyang<redacted>

---
 net/ipv6/udp.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index a6aecf7..e553ab7 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c

@@ -733,6 +733,9 @@ do_udp_sendmsg:
 	}
 
 	if (!fl.oif)
+		fl.oif = np->sticky_pktinfo.ipi6_ifindex;
+
+	if (!fl.oif)
 		fl.oif = sk->sk_bound_dev_if;
 
 	if (msg->msg_controllen) {

-- 
1.5.3.8