Merge branch 'enetc-ptp'

Yangbo Lu says:

====================
enetc: support PTP Sync packet one-step timestamping

This patch-set is to add support for PTP Sync packet one-step timestamping.
Since ENETC single-step register has to be configured dynamically per
packet for correctionField offeset and UDP checksum update, current
one-step timestamping packet has to be sent only when the last one
completes transmitting on hardware. So, on the TX, this patch handles
one-step timestamping packet as below:

- Trasmit packet immediately if no other one in transfer, or queue to
  skb queue if there is already one in transfer.
  The test_and_set_bit_lock() is used here to lock and check state.
- Start a work when complete transfer on hardware, to release the bit
  lock and to send one skb in skb queue if has.

Changes for v2:
	- Rebased.
	- Fixed issues from patchwork checks.
	- netif_tx_lock for one-step timestamping packet sending.
Changes for v3:
	- Used system workqueue.
	- Set bit lock when transmitted one-step packet, and scheduled
	  work when completed. The worker cleared the bit lock, and
	  transmitted one skb in skb queue if has, instead of a loop.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>