* origin/pr/2854:
Shorter version of mbedtls_ssl_send_fatal_handshake_failure
Resolve#2801 - remove repetitive assignment to ssl->in_msg (the first value was never used)
Resolve#2800 - move declaration to avoid unused variable warning in case MBEDTLS_SSL_PROTO_DTLS was undefined
Resolve#2717 - remove erroneous sizeof (the operator was applied to constant integer number)