Fixed key setup problem with AES PSK encryption

Nonce byte ordering corrected where it's passed to mbedtls_pkcs5_pbkdf2_hmac(). Verified against TR06 Appendix B test vector.

Nonce byte order on the wire corrected to match TR06 section 7.2 and Appendix B. Fixed same issue on send and receive side.

Corrected broken crypto output by removing call to mbedtls_aes_setkey_dec().

Note: reviewed and corrected only the USE_MBEDTLS case as this was relevant to our environment.