Merge branch 'sfc-Add-XDP-support'

Charles McLachlan says:

====================
sfc: Add XDP support

Supply the XDP callbacks in netdevice ops that enable lower level processing
of XDP frames.

Changes in v4:
- Handle the failure to send some frames in efx_xdp_tx_buffers() properly.

Changes in v3:
- Fix a BUG_ON when trying to allocate piobufs to xdp queues.
- Add a missed trace_xdp_exception.

Changes in v2:
- Use of xdp_return_frame_rx_napi() in tx.c
- Addition of xdp_rxq_info_valid and xdp_rxq_info_failed to track when
  xdp_rxq_info failures occur.
- Renaming of rc to err and more use of unlikely().
- Cut some duplicated code and fix an array overrun.
- Actually increment n_rx_xdp_tx when packets are transmitted.
====================

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