net: ipv4: Hook into time based transmission

Add a transmit_time field to struct inet_cork, then copy the
timestamp from the CMSG cookie at ip_setup_cork() so we can
safely copy it into the skb later during __ip_make_skb().

For the raw fast path, just perform the copy at raw_send_hdrinc().

Signed-off-by: Richard Cochran <rcochran@linutronix.de>
Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_sock.h

@@ -148,6 +148,7 @@ struct inet_cork {
 	__s16			tos;
 	char			priority;
 	__u16			gso_size;
+	u64			transmit_time;
 };
 
 struct inet_cork_full {