[B.A.T.M.A.N.] batman-adv debug logging (v2)

Hi,

I worked through the received feedback (thanks!) my first set of patches provoked and improved the code. The following changes have been made: * the log level no longer is a global variable and can be configured for each mesh individually * the "unused variable" warnings have been eliminated * now dead batctl code has been removed

I also considered making the debug log available via the standard kernel logging facilities but right now I can only see little value in this feature. We can still add it as soon as somebody complains.

Unless there are futher comments I will go ahead and commit the changes.

Regards, Marek