X509: Remove MBEDTLS_SSL_PREVERIFY_CB

Add a callback typedef 
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 55d145a..c87b370 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4625,16 +4625,15 @@
             ca_crl   = ssl->conf->ca_crl;
         }
 
-        /*
-         * Main check: verify certificate
-         */
-#if defined(MBEDTLS_SSL_PREVERIFY_CB)
         if( ssl->conf->f_pre_vrfy != NULL )
         {
             ssl->conf->f_pre_vrfy( ssl->conf->p_pre_vrfy,
                                    ssl->session_negotiate->peer_cert );
         }
-#endif
+
+        /*
+         * Main check: verify certificate
+         */
         ret = mbedtls_x509_crt_verify_with_profile(
                                 ssl->session_negotiate->peer_cert,
                                 ca_chain, ca_crl,
@@ -5884,17 +5883,15 @@
     conf->f_vrfy      = f_vrfy;
     conf->p_vrfy      = p_vrfy;
 }
-#endif /* MBEDTLS_X509_CRT_PARSE_C */
 
-#if defined(MBEDTLS_SSL_PREVERIFY_CB)
-void mbedtls_ssl_conf_pre_verify(mbedtls_ssl_config *conf,
-                             void(*f_pre_vrfy)(void *, mbedtls_x509_crt *),
-                             void *p_pre_vrfy)
+void mbedtls_ssl_conf_pre_verify( mbedtls_ssl_config *conf,
+                         mbedtls_ssl_pre_verify_t *f_pre_vrfy,
+                         void *p_pre_vrfy)
 {
   conf->f_pre_vrfy = f_pre_vrfy;
   conf->p_pre_vrfy = p_pre_vrfy;
 }
-#endif /* MBEDTLS_SSL_PREVERIFY_CB */
+#endif /* MBEDTLS_X509_CRT_PARSE_C */
 
 void mbedtls_ssl_conf_rng( mbedtls_ssl_config *conf,
                   int (*f_rng)(void *, unsigned char *, size_t),