net: export time stamp utility function for Ethernet MAC drivers

The network stack provides the function, skb_clone_tx_timestamp().
Ethernet MAC drivers can call this via the transmit time stamping
hook, skb_tx_timestamp(). This commit exports the clone function so
that drivers using it can be compiled as modules.

Signed-off-by: Richard Cochran <richard.cochran@omicron.at>
Signed-off-by: David S. Miller <davem@conan.davemloft.net>
diff --git a/net/core/timestamping.c b/net/core/timestamping.c
index 7e7ca37..3b00a6b 100644
--- a/net/core/timestamping.c
+++ b/net/core/timestamping.c
@@ -68,6 +68,7 @@
 		break;
 	}
 }
+EXPORT_SYMBOL_GPL(skb_clone_tx_timestamp);
 
 void skb_complete_tx_timestamp(struct sk_buff *skb,
 			       struct skb_shared_hwtstamps *hwtstamps)