net: Add export.h for EXPORT_SYMBOL/THIS_MODULE to non-modules

These files are non modular, but need to export symbols using
the macros now living in export.h -- call out the include so
that things won't break when we remove the implicit presence
of module.h from everywhere.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/net/core/timestamping.c b/net/core/timestamping.c
index 82fb288..661b5a4 100644
--- a/net/core/timestamping.c
+++ b/net/core/timestamping.c
@@ -21,6 +21,7 @@
 #include <linux/phy.h>
 #include <linux/ptp_classify.h>
 #include <linux/skbuff.h>
+#include <linux/export.h>
 
 static struct sock_filter ptp_filter[] = {
 	PTP_FILTER