Added sefun for seteuid()

As replacement for the efun seteuid() that was removed in the
driver.

Change-Id: Ic80c53838559a9a1f705e6023805f07e0a827432
diff --git a/sys/configuration.h b/sys/configuration.h
index b2c0b88..8ca189e 100644
--- a/sys/configuration.h
+++ b/sys/configuration.h
@@ -23,6 +23,7 @@
  */
 #define OC_COMMANDS_ENABLED    0
 #define OC_HEART_BEAT          1
+#define OC_EUID                2
 
 /* Possible options for configure_driver().
  */