Add certificate policy oid x509 extension

Add the `MBEDTLS_OID_X509_EXT_CERTIFICATE_POLICIES` to the list
of supported x509 extensions, in `mbedtls_oid_get_x509_ext_type()`.
diff --git a/tests/suites/test_suite_oid.function b/tests/suites/test_suite_oid.function
index 59e700e..890ffec 100644
--- a/tests/suites/test_suite_oid.function
+++ b/tests/suites/test_suite_oid.function
@@ -55,3 +55,26 @@
     }
 }
 /* END_CASE */
+
+/* BEGIN_CASE */
+void oid_get_x509_extension( data_t *oid, int exp_type )
+{
+    mbedtls_asn1_buf ext_oid = { 0, 0, NULL };
+    int ret;
+    int ext_type;
+
+    ext_oid.tag = MBEDTLS_ASN1_OID;
+    ext_oid.p = oid->x;
+    ext_oid.len = oid->len;
+
+    ret = mbedtls_oid_get_x509_ext_type( &ext_oid, &ext_type );
+    if( exp_type == 0 )
+    {
+        TEST_ASSERT( ret == MBEDTLS_ERR_OID_NOT_FOUND );
+    }
+    else
+    {
+        TEST_ASSERT( ext_type == exp_type );
+    }
+}
+/* END_CASE */