api: fix build without CMD_NET support

Provide stubs in case that no NET interface is supported.

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
diff --git a/api/api_net.c b/api/api_net.c
index 3f52d71..7b3805e 100644
--- a/api/api_net.c
+++ b/api/api_net.c
@@ -25,6 +25,7 @@
 
 #define errf(fmt, args...) do { printf("ERROR @ %s(): ", __func__); printf(fmt, ##args); } while (0)
 
+#ifdef CONFIG_CMD_NET
 
 static int dev_valid_net(void *cookie)
 {
@@ -85,3 +86,32 @@
 
 	return eth_receive(buf, len);
 }
+
+#else
+
+int dev_open_net(void *cookie)
+{
+	return API_ENODEV;
+}
+
+int dev_close_net(void *cookie)
+{
+	return API_ENODEV;
+}
+
+int dev_enum_net(struct device_info *di)
+{
+	return 0;
+}
+
+int dev_write_net(void *cookie, void *buf, int len)
+{
+	return API_ENODEV;
+}
+
+int dev_read_net(void *cookie, void *buf, int len)
+{
+	return API_ENODEV;
+}
+
+#endif