Merge branch 'timestamping'

Merge branch 'timestamping'

Alexander Duyck says:

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This change makes it so that the core path for the phy timestamping logic
is shared between skb_tx_tstamp and skb_complete_tx_timestamp.  In addition
it provides a means of using the same skb clone type path in non phy
timestamping drivers.

The main motivation for this is to enable non-phy drivers to be able to
manipulate tx timestamp skbs for such things as putting them in lists or
setting aside buffer in the context block.

v2: Incorporated suggested changes from Willem de Bruijn and Eric Dumazet
     dropped uneeded comment
     restored order of hwtstamp vs swtstamp
     added destructor for skb
    Dropped usage of skb_complete_tx_timestamp as a kfree_skb w/ destructor

v3: Updated destructor handling and dealt with socket reference counting issues

v4: Split out combining destructors into a separate patch
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