fix TLS Certificate CommonName NULL Byte Vulnerability

CVE-2020-7043 TLS Certificate CommonName NULL Byte Vulnerability is fixed
with this commit

with #8 hostname validation for the certificate was introduced
but unfortunately strncasecmp() was used to compare the byte array
against the expected hostname. This does not correctly treat a CN
which contains a NULL byte. In order to fix this vulnerability
the reference implementation from iSECPartners has been included
into the code.