libcxgb: Don't accidentally set RTO_ONLINK in cxgb_find_route()

Mask the ECN bits before calling ip_route_output_ports(). The tos
variable might be passed directly from an IPv4 header, so it may have
the last ECN bit set. This interferes with the route lookup process as
ip_route_output_key_hash() interpretes this bit specially (to restrict
the route scope).

Found by code inspection, compile tested only.

Fixes: 804c2f3e36 ("libcxgb,iw_cxgb4,cxgbit: add cxgb_find_route()")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/chelsio/libcxgb/libcxgb_cm.c

@@ -32,6 +32,7 @@
 
 #include <linux/tcp.h>
 #include <linux/ipv6.h>
+#include <net/inet_ecn.h>
 #include <net/route.h>
 #include <net/ip6_route.h>
 
@@ -99,7 +100,7 @@ cxgb_find_route(struct cxgb4_lld_info *lldi,
 
 	rt = ip_route_output_ports(&init_net, &fl4, NULL, peer_ip, local_ip,
 				   peer_port, local_port, IPPROTO_TCP,
-				   tos, 0);
+				   tos & ~INET_ECN_MASK, 0);
 	if (IS_ERR(rt))
 		return NULL;
 	n = dst_neigh_lookup(&rt->dst, &peer_ip);