utils/px5g-wolfssl: make selfsigned certicates compatible with chromium

utils/px5g-wolfssl: make selfsigned certicates compatible with chromium

Chromium based web-browsers (version >58) checks x509v3 extended attributes.
If this check fails then chromium does not allow to click "Proceed to ...
(unsafe)" link. This patch add three x509v3 extended attributes to self-signed
certificate:
1. SAN (Subject Alternative Name) (DNS Name) = CN (common name)
2. Key Usage = Digital Signature, Non Repudiation, Key Encipherment
3. Extended Key Usage = TLS Web Server Authentication

SAN will be added only if CONFIG_WOLFSSL_ALT_NAMES=y

Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>