add settings to set default freq at boot
more cc1101 config

add getpreamblelen
add comments

Enable by setting the IFF_TAP flag instead of the IFF_TUN flag in ifr_flags.

New interface allows checking if RTC time has been set.  This allows to application to detect if RTC has valid time (after
reset) or should application attempt to get real time by other means (for example, by launching ntpclient or GPS).

drivers/sensors: Add driver for ST LIS2DH accelerometer.  From Timo Voutilainen <time.voutilainen@haltian.com> et al.

From Harri Luhtala <harri.luhtala@haltian.com>. Tested with earlier
version of NuttX; with current version checked that it compiles.

Entropy pool gathers environmental noise from device drivers, user-space, etc., and returns good random numbers, suitable for cryptographic use. Based on entropy pool design from *BSDs and uses BLAKE2Xs algorithm for CSPRNG output.

Patch also adds /dev/urandom support for using entropy pool RNG and new 'getrandom' system call for getting randomness without file-descriptor usage (thus avoiding file-descriptor exhaustion attacks). The 'getrandom' interface is similar as 'getentropy' and 'getrandom' available on OpenBSD and Linux respectively.