Add support for OCSP stapling to validate server certificate

Add support for OCSP stapling to validate server certificate

When using OpenSSL with TLS-based EAP methods, wpa_supplicant can now be
configured to use OCSP stapling (TLS certificate status request) with
ocsp=1 network block parameter. ocsp=2 can be used to require valid OCSP
response before connection is allowed to continue.

hostapd as EAP server can be configured to return cached OCSP response
using the new ocsp_stapling_response parameter and an external mechanism
for updating the response data (e.g., "openssl ocsp ..." command).

This allows wpa_supplicant to verify that the server certificate has not
been revoked as part of the EAP-TLS/PEAP/TTLS/FAST handshake before
actual data connection has been established (i.e., when a CRL could not
be fetched even if a distribution point were specified).

Signed-hostap: Jouni Malinen <j@w1.fi>