Integrates optimized version of Micro-ECC

• Integrates optimized version of Micro-ECC open-source software (BSD 2 clauses License)
• AES-CCM mode was not correctly cleaning the output buffer in case of decryption failure as it had no means to know its length (this buffer has variable length, depending on mac and payload size). After this change, the caller now needs to explicitly pass the output buffer length as a parameter, allowing us to clean it in case of decryption failure.
• In the same spirit as done for the ECC key generation FIPS 186-4 (Appendix B.4.1) compliance, we improved EC-DSA signature generation to be FIPS 184-4 (Appendix B.5.1) compliant.
• Both improvements come at very marginal performance impact. For the ECC algorithms, for example, FIPS compliance represents not even 1% higher latency, thus we considered their integration as quite reasonable.
• The overall performance of our ECC algorithms are now competitive.
• Previous calculation of a shared secret (LESC DHKey) was unacceptable for production use and this latest release aims to significantly improve performance.