timestamping: fix example build

Fix Makefiles so that Documentation/networking/timestamping/timestamping.c
will build when using the CONFIG_BUILD_DOCSRC kconfig option.
(timestamping.c does not build currently with its simple Makefile.)

Also fix printf format warnings.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/networking/Makefile b/Documentation/networking/Makefile
index 6d8af1a..5aba7a3 100644
--- a/Documentation/networking/Makefile
+++ b/Documentation/networking/Makefile
@@ -6,3 +6,5 @@
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
+
+obj-m := timestamping/