bonding: add netlink attributes to slave link dev

If link is IFF_SLAVE, extend link dev netlink attributes to include
slave attributes with new IFLA_SLAVE nest.  Add netlink notification
(RTM_NEWLINK) when slave status changes from backup to active, or
visa-versa.

Adds new ndo_get_slave op to net_device_ops to fill skb with IFLA_SLAVE
attributes.  Currently only used by bonding driver, but could be
used by other aggregating devices with slaves.

Signed-off-by: Scott Feldman <sfeldma@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/if_link.h

@@ -144,6 +144,7 @@ enum {
 	IFLA_NUM_RX_QUEUES,
 	IFLA_CARRIER,
 	IFLA_PHYS_PORT_ID,
+	IFLA_SLAVE,
 	__IFLA_MAX
 };
 
@@ -368,6 +369,18 @@ enum {
 
 #define IFLA_BOND_AD_INFO_MAX	(__IFLA_BOND_AD_INFO_MAX - 1)
 
+enum {
+	IFLA_SLAVE_STATE,
+	IFLA_SLAVE_MII_STATUS,
+	IFLA_SLAVE_LINK_FAILURE_COUNT,
+	IFLA_SLAVE_PERM_HWADDR,
+	IFLA_SLAVE_QUEUE_ID,
+	IFLA_SLAVE_AD_AGGREGATOR_ID,
+	__IFLA_SLAVE_MAX,
+};
+
+#define IFLA_SLAVE_MAX	(__IFLA_SLAVE_MAX - 1)
+
 /* SR-IOV virtual function management section */
 
 enum {