libcurl did not check the server certificate of TLS connections done to a host
specified as an IP address, when built to use mbedTLS.
libcurl would wrongly avoid using the set hostname function when the specified
hostname was given as an IP address, therefore completely skipping the
certificate check. This affects all uses of TLS protocols (HTTPS, FTPS, IMAPS,
POPS3, SMTPS, etc).