IB/hfi1: Fix WQ_MEM_RECLAIM warning

The work_item cancels that occur when a QP is destroyed can elicit the
following trace:

 workqueue: WQ_MEM_RECLAIM ipoib_wq:ipoib_cm_tx_reap [ib_ipoib] is flushing !WQ_MEM_RECLAIM hfi0_0:_hfi1_do_send [hfi1]
 WARNING: CPU: 7 PID: 1403 at kernel/workqueue.c:2486 check_flush_dependency+0xb1/0x100
 Call Trace:
  __flush_work.isra.29+0x8c/0x1a0
  ? __switch_to_asm+0x40/0x70
  __cancel_work_timer+0x103/0x190
  ? schedule+0x32/0x80
  iowait_cancel_work+0x15/0x30 [hfi1]
  rvt_reset_qp+0x1f8/0x3e0 [rdmavt]
  rvt_destroy_qp+0x65/0x1f0 [rdmavt]
  ? _cond_resched+0x15/0x30
  ib_destroy_qp+0xe9/0x230 [ib_core]
  ipoib_cm_tx_reap+0x21c/0x560 [ib_ipoib]
  process_one_work+0x171/0x370
  worker_thread+0x49/0x3f0
  kthread+0xf8/0x130
  ? max_active_store+0x80/0x80
  ? kthread_bind+0x10/0x10
  ret_from_fork+0x35/0x40

Since QP destruction frees memory, hfi1_wq should have the WQ_MEM_RECLAIM.

The hfi1_wq does not allocate memory with GFP_KERNEL or otherwise become
entangled with memory reclaim, so this flag is appropriate.

Fixes: 0a226edd

 ("staging/rdma/hfi1: Use parallel workqueue for SDMA engines")
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>