BoringSSL: Fix session resumption

BoringSSL commit 533ef7304d9b48aad38805f1997031a0a034d7fe ('Remove
SSL_clear calls in handshake functions.') triggered a regression for
EAP-TLS/TTLS/PEAP session resumption in wpa_supplicant due to the
removed SSL_clear() call in ssl3_connect() going away and wpa_supplicant
not calling SSL_clear() after SSL_shutdown(). Fix this by adding the
SSL_clear() call into wpa_supplicant after SSL_shutdown() when preparing
the ssl instance for another connection.

While OpenSSL is still call SSL_clear() in ssl3_connect(), it looks to
be safe to add this call to wpa_supplicant unconditionally.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/crypto/tls_openssl.c

@@ -1142,7 +1142,7 @@ int tls_connection_shutdown(void *ssl_ctx, struct tls_connection *conn)
 	 * and "close notify" shutdown alert would confuse AS. */
 	SSL_set_quiet_shutdown(conn->ssl, 1);
 	SSL_shutdown(conn->ssl);
-	return 0;
+	return SSL_clear(conn->ssl) == 1 ? 0 : -1;
 }