test: the JSON generators against the tables the CLI wrote

page_impl.c and rtl837x_port.c are linked together over the simulated
engine, so /vlan.json, /vlanlist and /l2.json are checked against what
vlan_create, pvid and the L2 table hold, through the same bytes the switch
would. The L2 walk is driven the way the web page drives it, page after
page until an index repeats, which is also where the repeat of the first
entry is pinned down as the wrap marker the page relies on. The counter
test fails on the code before the previous commit.

test/Makefile

@@ -25,7 +25,8 @@ BUILDDIR = build
 
 # One binary per subsystem under test.
 TESTS = $(BUILDDIR)/test_cmd_editor \
-        $(BUILDDIR)/test_port_tables
+        $(BUILDDIR)/test_port_tables \
+        $(BUILDDIR)/test_page_json
 
 # The table tests link the register mock and one environment file; stub/
 # stands in for the two headers a firmware build generates.
@@ -45,6 +46,9 @@ $(BUILDDIR)/test_cmd_editor: test_cmd_editor.c support.c $(SRCROOT)/cmd_editor.c
 $(BUILDDIR)/test_port_tables: test_port_tables.c $(TABLE_ENV) hw_mock.h | $(BUILDDIR)
 	$(CC) $(CFLAGS) $(filter %.c,$^) -o $@ $(LDFLAGS)
 
+$(BUILDDIR)/test_page_json: test_page_json.c $(TABLE_ENV) hw_mock.h | $(BUILDDIR)
+	$(CC) $(CFLAGS) $(filter %.c,$^) -o $@ $(LDFLAGS)
+
 run: $(TESTS)
 	@fail=0; for t in $(TESTS); do \
 		echo "=== $$t ==="; \