netd: Implement tty lists and tty validation

Signed-off-by: San Mehat <san@google.com>
diff --git a/PppController.h b/PppController.h
index 8683de2..5046822 100644
--- a/PppController.h
+++ b/PppController.h
@@ -37,6 +37,7 @@
     TtyCollection *getTtyList();
 
 private:
+    int updateTtyList();
 };
 
 #endif