net-timestamp: SCHED timestamp on entering packet scheduler

Kernel transmit latency is often incurred in the packet scheduler.
Introduce a new timestamp on transmission just before entering the
scheduler. When data travels through multiple devices (bonding,
tunneling, ...) each device will export an individual timestamp.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/linux/skbuff.h
Simple merge

diff --cc include/uapi/linux/errqueue.h
Simple merge

diff --cc include/uapi/linux/net_tstamp.h
Simple merge

diff --cc net/core/dev.c
Simple merge

diff --cc net/core/skbuff.c
Simple merge

diff --cc net/socket.c
Simple merge