vxlan: fix populating tclass in vxlan6_get_route

Jiri mentioned that flowi6_tos of struct flowi6 is never used/read
anywhere. In fact, rest of the kernel uses the flowi6's flowlabel,
where the traffic class _and_ the flowlabel (aka flowinfo) is encoded.

For example, for policy routing, fib6_rule_match() uses ip6_tclass()
that is applied on the flowlabel member for matching on tclass. Similar
fix is needed for geneve, where flowi6_tos is set as well. Installing
a v6 blackhole rule that f.e. matches on tos is now working with vxlan.

Fixes: 1400615d64 ("vxlan: allow setting ipv6 traffic class")
Reported-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ipv6.h

@@ -835,6 +835,12 @@ static inline u8 ip6_tclass(__be32 flowinfo)
 {
 	return ntohl(flowinfo & IPV6_TCLASS_MASK) >> IPV6_TCLASS_SHIFT;
 }
+
+static inline __be32 ip6_make_flowinfo(unsigned int tclass, __be32 flowlabel)
+{
+	return htonl(tclass << IPV6_TCLASS_SHIFT) | flowlabel;
+}
+
 /*
  *	Prototypes exported by ipv6
  */