lwip: tls: warn when no CA exists amd log certificate validation errors

Using HTTPS without root (CA) certificates is a security issue. Print a
warning in this case. Also, when certificate verification fail, print
an additional message because "HTTP client error 4" is not very
informative (4 is HTTPC_RESULT_ERR_CLOSED).

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
1 file changed