Staging: batman-adv: Update TODO with new points from review

David S. Miller provided some new ideas and found problems in his review
20100719.212625.255369607.davem@davemloft.net. These issues must be
resolved before it can be merged into net.

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