clean up native hwtimer
fix native hwtimer unsetting

reverts bug introduced by 2bfb062
Merge pull request #420 from LudwigOrtmann/native_hwtimer_fixup

Native hwtimer fixup
use CC1100_NOBYTE consistently (fixing #129)
Merge pull request #422 from OlegHahm/nobyte

use CC1100_NOBYTE consistently (fixing #129)