Staging: batman-adv: move /proc interface handling to /sys

Instead of having a single /proc file "interfaces" in which you have
to echo the wanted interface batman-adv will create a subfolder in each
suitable /sys/class/net folder. This subfolder contains files for the
interface specific settings. For example, mesh_iface to add/remove an
interface from a virtual mesh network (at the moment only bat0 is
supported).

Example:
echo bat0 > /sys/class/net/eth0/batman-adv/mesh_iface

to deactivate:
echo none > /sys/class/net/eth0/batman-adv/mesh_iface

Interfaces which are not compatible with batman-adv won't contain the
batman-adv folder, therefore can't be activated. Not supported are:
loopback, non-ethernet, non-ARP and virtual mesh network interfaces

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>