net: lwip: add TFTP support and tftpboot command

Implement do_tftpb(). This implementation of the tftp command
supports an optional port number. For example:

 tftp 192.168.0.30:9069:file.bin

It also supports taking the server IP from ${tftpserverip} if
defined, before falling back to ${serverip}.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/include/net-lwip.h b/include/net-lwip.h
index cfd0672..37744b0 100644
--- a/include/net-lwip.h
+++ b/include/net-lwip.h
@@ -6,6 +6,10 @@
 #include <lwip/ip4.h>
 #include <lwip/netif.h>
 
+enum proto_t {
+	TFTPGET
+};
+
 struct netif *net_lwip_new_netif(struct udevice *udev);
 struct netif *net_lwip_new_netif_noip(struct udevice *udev);
 void net_lwip_remove_netif(struct netif *netif);