[B.A.T.M.A.N.] Various fixes and clean-ups

["Linus Lüssing" <linus.luessing@web.de>]

Hi everyone,

For one thing, I've changed the orig_node->router dereference as discussed on IRC,
now using an extra getter method for that to reduce the lines of code for
rcu-dereferencing, rcu-locking and refcounting for the router pointer
and to make it easier to keep track of the right refcounting (Patch 4/5). Note,
that the previous version was pretty simple, by just using rcu_dereference() everywhere.
However, this current version is a little more invasive, so would be great if
someone could double check that I didn't introduce any new mem-leaks or
null-pointer-dereferences due to wrong refcounting. It already took me quite
some time to find and squash two bugs I had introduced with this, so
there might be even more in there. I double checked it myself and
also tested it in a 4 node chain toplogy vm setup, though.

For Patch 5/5, I've removed the "TQ value" from the patch subject. For the TQ
window locking is definitely needed, whether tq_avg needs locking as well still
needs to be checked. If so, that could be done with a separate patch though.

Patches 1,2,3 are just some smaller changes. Let me know what you think about them.

Cheers, Linus