This reduces the average CPU consumption (on a WDR4300) from 3% to 1%.
Also, this commit adds error messages when the parsing fails and makes matching
more flexible after all relevant fields have been found.
This package drops all incoming router advertisements except for the
default router with the best metric according to B.A.T.M.A.N. advanced.
Note that advertisements originating from the node itself (for example
via gluon-radvd) are not affected.
