batman-adv: Add get_ethtool_stats() support

Added additional counters in a bat_stats structure, which are exported
through the ethtool api. The counters are specific to batman-adv and
includes:
 forwarded packets and bytes
 management packets and bytes (aggregated OGMs at this point)
 translation table packets

New counters are added by extending "enum bat_counters" in types.h and
adding corresponding  descriptive string(s) to bat_counters_strings in
soft-iface.c.

Counters are increased by calling batadv_add_counter() and incremented
by one by calling batadv_inc_counter().

Signed-off-by: Martin Hundebøll <martin@hundeboll.net>
Signed-off-by: Sven Eckelmann <sven@narfation.org>

net/batman-adv/main.c

@@ -153,6 +153,8 @@ void mesh_free(struct net_device *soft_iface)
 
 	bla_free(bat_priv);
 
+	free_percpu(bat_priv->bat_counters);
+
 	atomic_set(&bat_priv->mesh_state, MESH_INACTIVE);
 }