Update U-Boot's build timestamp on every compile

Use the GNU 'date' command to auto-generate a new U-Boot
timestamp on every compile.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/net/net.c b/net/net.c
index 77e83b5..e9754e4 100644
--- a/net/net.c
+++ b/net/net.c
@@ -89,6 +89,9 @@
 #if defined(CONFIG_CMD_SNTP)
 #include "sntp.h"
 #endif
+#if defined(CONFIG_CDP_VERSION)
+#include <timestamp.h>
+#endif
 
 #if defined(CONFIG_CMD_NET)