* Updates driver library to v2.3.1 (2018q1) for bugfixes and convenience functions
* Provides library in correct format (2-byte wchar_t flag) for compiling with ARMCC (#6695 uncovered by #6577)
* Reverts to using a statically-allocated packet buffer since malloc is not thread-safe (and the asserts have been turned on)
Due to limitation in the mbed website backend (board names need to be <= 19 characters), we are shortening the CLI target names from THUNDERBOARD to TB.
@screamerbg
As asked by @0xc0170 in PR #3934, we won't be using device_has for indicating RF/Crypto features any longer. RF config options moved to the SL_RAIL lib.json, crypto config options will come with mbedTLS integration.
mbed compile doesn't support two different FEATURE_X folders being merged, so we'll have to move our nanostack driver into the Nanostack folder for the time being.