[B.A.T.M.A.N.] RFC: Unicasting multicast reports to querier-node only

WARNING: The following patches were only compile-time tested - you've been warned ;).

The last round of multicast patches to add support for the multicast optimizations in bridged scenarios, too, unfortunately had one major conceptual flaw: It could lead to packet loss. It's not sufficient to have the unicasting of reports implemented on bridge-nodes only. Nodes without bridges need to treat reports the same way.

The issue is described in detail here:

https://www.open-mesh.org/projects/batman-adv/wiki/Multicast-optimizations-l...

These patches are one suggestion to tackle this issue (alternatives can be found on the wikipage, too). Let me know what you think about this approach.

Cheers, Linus