Fix warning differ in signedness in net/net.c and net/nfs.c
diff --git a/net/bootp.h b/net/bootp.h
index ba9826e..320cc3b 100644
--- a/net/bootp.h
+++ b/net/bootp.h
@@ -88,7 +88,7 @@
 #define DHCP_NAK      6
 #define DHCP_RELEASE  7
 
-#define SELECT_TIMEOUT 3	/* Seconds to wait for offers */
+#define SELECT_TIMEOUT 3UL	/* Seconds to wait for offers */
 
 /**********************************************************************/