Staging: batman-adv: Move device for icmp injection to debugfs

batctl uses /dev/batman-adv to send special batman-adv icmp packets to
other nodes in the mesh. To get it working with multiple batX devices we
must ensure that every mesh device can have their own socket which is
used to inject those packets in exactly one mesh.

The current implementation still doesn't allow to use complete separated
meshes as we rely on structures which are not part of the private data
of a batman device.

Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>