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>

net/wget.c

@@ -404,6 +404,7 @@ static void wget_handler(uchar *pkt, u16 dport,
 		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;
 	}
 }