[BRIDGE]: Disable SG/GSO if TX checksum is off

When the bridge recomputes features, it does not maintain the
constraint that SG/GSO must be off if TX checksum is off.
This patch adds that constraint.

On a completely unrelated note, I've also added TSO6 and TSO_ECN
feature bits if GSO is enabled on the underlying device through
the new NETIF_F_GSO_SOFTWARE macro.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index c0c2b46..50a4719 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -320,6 +320,9 @@
 #define NETIF_F_TSO_ECN		(SKB_GSO_TCP_ECN << NETIF_F_GSO_SHIFT)
 #define NETIF_F_TSO6		(SKB_GSO_TCPV6 << NETIF_F_GSO_SHIFT)
 
+	/* List of features with software fallbacks. */
+#define NETIF_F_GSO_SOFTWARE	(NETIF_F_TSO | NETIF_F_TSO_ECN | NETIF_F_TSO6)
+
 #define NETIF_F_GEN_CSUM	(NETIF_F_NO_CSUM | NETIF_F_HW_CSUM)
 #define NETIF_F_ALL_CSUM	(NETIF_F_IP_CSUM | NETIF_F_GEN_CSUM)