net/mlx5e: xsk: Use partial batches in legacy RQ with XSK

The previous commit allowed allocating WQE batches in legacy RQ
partially, however, XSK still checks whether there are enough frames in
the fill ring. Remove this check to allow to allocate batches partially
also with XSK.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>