If a UMEM is present on a queue when an interface/queue pair is being
enabled, the driver will try to prepare the Rx buffers in advance to
improve performance. However, if fill queue is shorter than HW Rx ring,
the driver will report failure after getting the last address from the
fill queue.

This still lets the driver process the packets correctly during the NAPI
poll, but leads to a constant NAPI rescheduling. Not allocating the
buffers in advance would result in a potential performance decrease.

Commit d57d7642 ("xsk: Add API to check for available entries in FQ")
provides an API that lets drivers check the number of addresses that the
fill queue holds.

Notify the user if fill queue is not long enough to prepare all buffers
before packet processing starts, and allocate the buffers during the
NAPI poll. If the fill queue size is sufficient, prepare Rx buffers in
advance.
Signed-off-by: Krzysztof Kazimierczak <krzysztof.kazimierczak@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>