Staging: batman-adv: permit setting ogm interval to JITTER*2

When trying to set the originator interval to 40ms, we are asked to set
it to a minimum value of 40ms. This patch permits setting an
originator interval of JITTER*2 (40ms by default) now.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>