Fixed some of the targets broken by changing the UIP_CONF_LLH_LEN default.

https://github.com/contiki-os/contiki/commit/c0b3c87ba757b949aadfe20c3fcbc701c3ce192b changed the default of `UIP_CONF_LLH_LEN` from `14` to `0`. This broke of course all targets relying on the default :-(

BTW: I can't see a pull request for the change in question. So I was only afterwards made aware of it because of my subscription of contiki-commits-request@lists.sourceforge.net :-((