net/wget: set filesize

After downloading a file with wget the file size may be needed in follow up
actions, e.g.

* write file to device
* calculate hash

Let wget set the environment variable filesize.

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/net/wget.c b/net/wget.c
index b4251e0..c9b8fc9 100644
--- a/net/wget.c
+++ b/net/wget.c
@@ -404,6 +404,7 @@
 		efi_set_bootdev("Net", "", image_url,
 				map_sysmem(image_load_addr, 0),
 				net_boot_file_size);
+		env_set_hex("filesize", net_boot_file_size);
 		break;
 	}
 }