Removed the unused function cc2420_cca_valid and replaced some macros with functions in CC2420. This reduces the code size with over 400 bytes.
Removed the unused function cc2420_cca_valid and replaced some macros
with functions in CC2420. This reduces the code size with over 400 bytes.

arurke/contiki,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr,bluerover/6lbr,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr,arurke/contiki,bluerover/6lbr,arurke/contiki,bluerover/6lbr,arurke/contiki,bluerover/6lbr,bluerover/6lbr,MohamedSeliem/contiki,MohamedSeliem/contiki