net: documentation: build a directory structure for drivers

Documentation/networking/ is full of cryptically named files with
driver documentation.  This makes finding interesting information
at a glance really hard.  Move all those files into a directory
called device_drivers (since not all drivers are for device) and
fix up references.

RFC v0.1 -> RFC v1:
 - also add .txt suffix to the files which are missing it (Quentin)

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: David Ahern <dsahern@gmail.com>
Acked-by: Henrik Austad <henrik@austad.us>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index d037751..6371958 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -397,10 +397,10 @@
 
 	  At present this driver only compiles as a module, so say M here if
 	  you have this card. The module will be called sb1000. Then read
-	  <file:Documentation/networking/README.sb1000> for information on how
-	  to use this module, as it needs special ppp scripts for establishing
-	  a connection. Further documentation and the necessary scripts can be
-	  found at:
+	  <file:Documentation/networking/device_drivers/sb1000.txt> for
+	  information on how to use this module, as it needs special ppp
+	  scripts for establishing a connection. Further documentation
+	  and the necessary scripts can be found at:
 
 	  <http://www.jacksonville.net/~fventuri/>
 	  <http://home.adelphia.net/~siglercm/sb1000.html>