examples/radio-scannable-broadcaster: Reorganize code & comments
examples/ll-broadcaster: Sanitize interval timeout
ll: Reorganize code in ll_advertise_start()
nrf51822/radio: Fix buffer overflow bug

The radio input buffer must be able to store a full packet with 39
octets. But the MAXLEN configuration of NRF_RADIO->PCNF1 register
stores the maximum length of PAYLOAD, which is 37 octets, and not
the full packet.
nrf51822/radio: Remove outdated/unnecessary comments
nrf51822/radio: Remove outdated comment
nrf51822/radio: Remove unnecessary crc variable
examples/timming: Add static modifier to local symbols
examples/radio-broadcaster: Add static modifier to local functions
examples/radio-passive-observer: Add static modifier to local functions
examples/radio-scannable-broadcaster: Add static modifier to local functions
examples/ll-scanner: Add static modifier to local functions
radio: Add radio_prepare() API
nrf51822/radio: Implement radio_prepare() API
radio: Remove ch/aa/crcinit params from radio_send/recv() APIs
examples: Replace radio_reply() by radio_send()
radio: Remove radio_reply() API
radio: Remove len parameter from radio_send() API
radio: Add flags parameter to radio_send() API
nrf51822/radio: Clear flags when stop the radio