Staging: batman-adv: Mark debugfs files as nonseekable

We don't allow to seek in the debugfs socket and log files. Thus we
should mark the file descriptor as nonseekable.

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