net: Include string.h in net-legacy.h

This file uses memcpy() but does not include the header file. Update it.

Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Simon Glass <sjg@chromium.org>

include/net-legacy.h

@@ -17,6 +17,7 @@
 #include <log.h>
 #include <time.h>
 #include <linux/if_ether.h>
+#include <linux/string.h>
 
 struct bd_info;
 struct cmd_tbl;