xfrm4: strip ECN bits from tos field

otherwise ECT(1) bit will get interpreted as RTO_ONLINK
and routing will fail with XfrmOutBundleGenError.

Signed-off-by: Ulrich Weber <uweber@astaro.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/xfrm4_policy.c b/net/ipv4/xfrm4_policy.c
index 869078d..a580349 100644
--- a/net/ipv4/xfrm4_policy.c
+++ b/net/ipv4/xfrm4_policy.c
@@ -61,7 +61,7 @@
 
 static int xfrm4_get_tos(struct flowi *fl)
 {
-	return fl->fl4_tos;
+	return IPTOS_RT_MASK & fl->fl4_tos; /* Strip ECN bits */
 }
 
 static int xfrm4_init_path(struct xfrm_dst *path, struct dst_entry *dst,