ice, xsk: Move Rx allocation out of while-loop

Instead doing the check for allocation in each loop, move it outside
the while loop and do it every NAPI loop.

This change boosts the xdpsock rxdrop scenario with 15% more
packets-per-second.

Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Link: https://lore.kernel.org/r/20201211085410.59350-1-bjorn.topel@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>