ipv6: sit: Unmask upper DSCP bits in ipip6_tunnel_xmit()

The function calls flowi4_init_output() to initialize an IPv4 flow key
with which it then performs a FIB lookup using ip_route_output_flow().

The 'tos' variable with which the TOS value in the IPv4 flow key
(flowi4_tos) is initialized contains the full DS field. Unmask the upper
DSCP bits so that in the future the FIB lookup could be performed
according to the full DSCP value.
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/sit.c

@@ -51,6 +51,7 @@
 #include <net/dsfield.h>
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
+#include <net/inet_dscp.h>
 
 /*
    This version of net/ipv6/sit.c is cloned of net/ipv4/ip_gre.c
@@ -935,8 +936,8 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
 	}
 
 	flowi4_init_output(&fl4, tunnel->parms.link, tunnel->fwmark,
-			   RT_TOS(tos), RT_SCOPE_UNIVERSE, IPPROTO_IPV6,
-			   0, dst, tiph->saddr, 0, 0,
+			   tos & INET_DSCP_MASK, RT_SCOPE_UNIVERSE,
+			   IPPROTO_IPV6, 0, dst, tiph->saddr, 0, 0,
 			   sock_net_uid(tunnel->net, NULL));
 
 	rt = dst_cache_get_ip4(&tunnel->dst_cache, &fl4.saddr);