RDMA/i40iw: Remove push code from i40iw

The push feature does not work as expected in x722 and has historically
been disabled in the driver.

Purge all remaining code related to the push feature in i40iw.

Link: https://lore.kernel.org/r/20201125005616.1800-3-shiraz.saleem@intel.com


Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>