Fixed native border router to compile and have less packet loss (due to slip-dev bug).

Native border router did not compile - which seems to be the normal case for most of the native platform examples - this is fixed via the makefile for the NBR. A very small but important bugfix of slip-dev so that it does not trash incoming data from slip-radio due to allocation of buffer on stack. Improved performance very very much when pushing NBR into higher speeds.