Staging: batman-adv: Fix resizing of broadcast seqno buffers on if deletion

Not only the entries of the deleted interface got erased, but also all
ones with a lower if_num. This commit fixes this issue by setting the
destination appropriately.

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