We still use the primary location by default (Info Page) but
this is now configurable. This change is useful for users who
wish to specify their own MAC address. Since the Info Page is
read-only, they need to be able to use the secondary location
Unlike cc2430, the cc2530 RF driver never generates interrupts.
This configuration in main() was a remnant of the porting from
the sensinode main, which does in fact need it.
Also updated comments in contiki-conf to reflect that shortcuts
don't influence the RF
