wolfssl: Fixes for building with OpenSSL compatibility layer

Resolves conflicts with building against wolfSSL when
`--enable-opensslextra` is set, namely the `WOLFSSL_HMAC_H_`,
`RNG` and `ASN1_*` name conflicts.

Closes strongswan/strongswan#151.

src/libstrongswan/plugins/wolfssl/wolfssl_diffie_hellman.h

@@ -25,8 +25,8 @@
  * @{ @ingroup wolfssl_p
  */
 
-#ifndef WOLFSSL_DIFFIE_HELLMAN_H_
-#define WOLFSSL_DIFFIE_HELLMAN_H_
+#ifndef WOLFSSL_PLUGIN_DIFFIE_HELLMAN_H_
+#define WOLFSSL_PLUGIN_DIFFIE_HELLMAN_H_
 
 typedef struct wolfssl_diffie_hellman_t wolfssl_diffie_hellman_t;
 
@@ -53,5 +53,5 @@ struct wolfssl_diffie_hellman_t {
 wolfssl_diffie_hellman_t *wolfssl_diffie_hellman_create(
 											diffie_hellman_group_t group, ...);
 
-#endif /** WOLFSSL_DIFFIE_HELLMAN_H_ @}*/
+#endif /** WOLFSSL_PLUGIN_DIFFIE_HELLMAN_H_ @}*/