nic: Fix incorrect wrap handling of RX circular buffer

nic: move other nic functions into the dedicated nic files
uip: alloc buffer multiple of 8 bytes

Signed-off-by: João Silva <jgc3silva@gmail.com>

test/Makefile

@@ -29,6 +29,7 @@ TESTS = $(BUILDDIR)/test_cmd_editor \
         $(BUILDDIR)/test_page_json \
         $(BUILDDIR)/test_httpd_tx \
         $(BUILDDIR)/test_tick_gate \
+        $(BUILDDIR)/test_nic_rx \
         $(BUILDDIR)/test_lacp
 
 # The table tests link the register mock and one environment file; stub/
@@ -52,6 +53,11 @@ $(BUILDDIR)/test_port_tables: test_port_tables.c $(TABLE_ENV) hw_mock.h | $(BUIL
 $(BUILDDIR)/test_tick_gate: test_tick_gate.c support.c $(SRCROOT)/cmd_editor.c | $(BUILDDIR)
 	$(CC) $(CFLAGS) $^ -o $@ $(LDFLAGS)
 
+# Exercise the production RX ring reader; only the hardware DMA edge is mocked.
+# Discard unused TX functions so this RX fixture needs no TX register mocks.
+$(BUILDDIR)/test_nic_rx: test_nic_rx.c $(SRCROOT)/rtl837x_nic.c $(SRCROOT)/rtl837x_nic.h | $(BUILDDIR)
+	$(CC) $(CFLAGS) -ffunction-sections -fdata-sections $(filter %.c,$^) -o $@ $(LDFLAGS) -Wl,--gc-sections
+
 $(BUILDDIR)/test_page_json: test_page_json.c $(TABLE_ENV) hw_mock.h | $(BUILDDIR)
 	$(CC) $(CFLAGS) $(filter %.c,$^) -o $@ $(LDFLAGS)