tdef: Introduce min_val and max_val fields

This is useful for timers expected to have a range of valid or expected
values.

Validation is done at runtime when timer values are set by the app or by
the user through the VTY.

Related: OS#4190
Change-Id: I4661ac41c29a009a1d5fc57d87aaee6041c7d1b2
diff --git a/tests/tdef/tdef_vty_test_config_root.c b/tests/tdef/tdef_vty_test_config_root.c
index d69e028..92113e8 100644
--- a/tests/tdef/tdef_vty_test_config_root.c
+++ b/tests/tdef/tdef_vty_test_config_root.c
@@ -55,6 +55,9 @@
 	{ .T=4, .default_val=100, .unit=OSMO_TDEF_CUSTOM, .desc="Testing a hundred potatoes" },
 	{ .T=0x7fffffff, .default_val=0xffffffff, .unit=OSMO_TDEF_M, .desc="Very large" },
 	{ .T=-23, .default_val=239471, .desc="Negative T number" },
+	{ .T=30, .default_val=50, .desc="Testing range min", .min_val=20 },
+	{ .T=31, .default_val=50, .desc="Testing range max", .max_val=52 },
+	{ .T=32, .default_val=50, .desc="Testing range both", .min_val=20, .max_val=52 },
 	{}  //  <-- important! last entry shall be zero
 };