net: expose eth_is_active() function to test network device state

The previous eth_device struct returned by eth_get_dev() allowed
code to directly query the state member field. However, with
CONFIG_DM_ETH this data gets encapsulated (i.e. private), and
eth_get_dev() returns a udevice struct 'abstraction' instead.

This breaks legacy code relying on the former behaviour - e.g.
netconsole.
(see http://lists.denx.de/pipermail/u-boot/2015-June/216528.html)

The patch introduces a method to retrieve the ethernet device
state in a 'clean' and uniform way, supporting both legacy code
and driver model. The new function eth_is_active() accepts a
device struct pointer and tests it for ETH_STATE_ACTIVE.

Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/include/net.h b/include/net.h
index f1671e3..3a787cc 100644
--- a/include/net.h
+++ b/include/net.h
@@ -149,7 +149,9 @@
  */
 struct udevice *eth_get_dev_by_name(const char *devname);
 unsigned char *eth_get_ethaddr(void); /* get the current device MAC */
+
 /* Used only when NetConsole is enabled */
+int eth_is_active(struct udevice *dev); /* Test device for active state */
 int eth_init_state_only(void); /* Set active state */
 void eth_halt_state_only(void); /* Set passive state */
 #endif
@@ -195,6 +197,8 @@
 	return NULL;
 }
 
+/* Used only when NetConsole is enabled */
+int eth_is_active(struct eth_device *dev); /* Test device for active state */
 /* Set active state */
 static inline __attribute__((always_inline)) int eth_init_state_only(void)
 {