net/mlx5e: Recover Send Queue (SQ) from error state

net/mlx5e: Recover Send Queue (SQ) from error state

An error TX completion (CQE) which arrived on a specific SQ indicates
that this SQ got moved by the hardware to error state, which means all
pending and incoming TX requests are dropped or will be dropped and no
further "Good" CQEs will be generated for that SQ.

Before this patch TX completions (CQEs) were not monitored and were
handled as a regular CQE. This caused the SQ to stay in an error state,
making it useless for xmiting new packets.

Mitigation plan:
In case of an error completion, schedule a recovery work which would do
the following:
- Mark the TXQ as DRV_XOFF to disable new packets to arrive from the
  stack
- NAPI to flush all pending SQ WQEs (via flush_in_error_en bit) to
  release SW and HW resources(SKB, DMA, etc) and have the SQ and CQ
  consumer/producer indices synced.
- Modify the SQ state ERR -> RST -> RDY (restart the SQ).
- Reactivate the SQ and reset SQ cc and pc

If we identify two consecutive requests for SQ recover in less than
500 msecs, drop the recover request to avoid CPU overload, as this
scenario most likely happened due to a severe repeated bug.

In addition, add SQ recover SW counter to monitor successful recoveries.

Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>