batman-adv: Add the backbone gateway list to debugfs

This is especially useful if there are no claims yet, but we still want
to know which gateways are using bridge loop avoidance in the network.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

Documentation/networking/batman-adv.txt

@@ -75,9 +75,10 @@ folder:
 
 There is a special folder for debugging information:
 
-#  ls /sys/kernel/debug/batman_adv/bat0/
-# bla_claim_table    log                socket             transtable_local
-# gateways           originators        transtable_global  vis_data
+# ls /sys/kernel/debug/batman_adv/bat0/
+# bla_backbone_table  log                 transtable_global
+# bla_claim_table     originators         transtable_local
+# gateways            socket              vis_data
 
 Some of the files contain all sort of status information  regard-
 ing  the  mesh  network.  For  example, you can view the table of