net: break include loop netdevice.h, dsa.h, devlink.h

There is an include loop between netdevice.h, dsa.h, devlink.h because
of NETDEV_ALIGN, making it impossible to use devlink structures in
dsa.h.

Break this loop by taking dsa.h out of netdevice.h, add a forward
declaration of dsa_switch_tree and netdev_set_default_ethtool_ops()
function, which is what netdevice.h requires.

No longer having dsa.h in netdevice.h means the includes in dsa.h no
longer get included. This breaks a few other files which depend on
these includes. Add these directly in the affected file.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/bcm_sf2_cfp.c

@@ -10,10 +10,11 @@
  */
 
 #include <linux/list.h>
-#include <net/dsa.h>
 #include <linux/ethtool.h>
 #include <linux/if_ether.h>
 #include <linux/in.h>
+#include <linux/netdevice.h>
+#include <net/dsa.h>
 #include <linux/bitmap.h>
 
 #include "bcm_sf2.h"

drivers/net/dsa/mv88e6xxx/mv88e6xxx.h

@@ -16,6 +16,7 @@
 #include <linux/irq.h>
 #include <linux/gpio/consumer.h>
 #include <linux/phy.h>
+#include <net/dsa.h>
 
 #ifndef UINT64_MAX
 #define UINT64_MAX		(u64)(~((u64)0))