HW flushes after QP in error state is not reliable. This can lead to
   application hang waiting on a completion for outstanding WRs.  Implement a
SW mechanism to generate completions for any outstanding WR's after the QP
is modified to error.

This is accomplished by starting a delayed worker after the QP is modified
to error and the HW flush is performed. The worker will generate
completions that will be returned to the application when it polls the
CQ. This mechanism only applies to Kernel applications.

Link: https://lore.kernel.org/r/20220425181624.1617-1-shiraz.saleem@intel.comSigned-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>