coap_openssl.c: Fix dtls typo  should be tls in coap_dtls_new_context()
coap_openssl.c: Fix dtls typo  should be tls in coap_dtls_new_context()

Correct parameter typo to SSL_CTX_set_cipher_list() from original TLS merge

authmillenon/libcoap,authmillenon/libcoap,authmillenon/libcoap