nrf51822/timer: Add code to check for too long intervals
with the current setup, max time is ~16s
timer: Add get_remaining_us() function to API
nrf51822/timer: Implement get_remaining_us()
ll: add connection index to public functions
ll: implement a map of current active connections
ll: check that the connection is active in public functions
ll: Refactor scan/init start functions to use the same code
ll: Add a secondary state to allow for simultaneous operations
i.e. connection & scanning or connection & initiating
ll: State verification in public functions
ll: use connection index in ll_on_radio_rx() and t_ll_interval_cb()
ll: implement timing management for multiple connections
Use of timeslots inside the main connection interval
ll: start and stop secondary operations in connection state
ll: Handle timing issues for the first connection events