net/tmpl_std: add Makefile for 'make regen'

Allow using "make regen" in the net dir to regenerate the configs, just
like it is possible to type "make regen" in the make dir.

This is a minor usability improvement, so one does not need to remember
to type ../fill_config.py in the net dir.

Change-Id: I8b23f8ae1f1d6ade597a30a222dfc82ea890d207
diff --git a/net/tmpl_std/Makefile b/net/tmpl_std/Makefile
new file mode 100644
index 0000000..62ae7a7
--- /dev/null
+++ b/net/tmpl_std/Makefile
@@ -0,0 +1,5 @@
+# Do nothing by default
+all:
+
+regen:
+	../fill_config.py