i40e: fix crash when Rx descriptor count is changed

When the AF_XDP buffer allocator was introduced, the Rx SW ring
"rx_bi" allocation was moved from i40e_setup_rx_descriptors()
function, and was instead done in the i40e_configure_rx_ring()
function.

This broke the ethtool set_ringparam() hook for changing the Rx
descriptor count, which was relying on i40e_setup_rx_descriptors() to
handle the allocation.

Fix this by adding an explicit i40e_alloc_rx_bi() call to
i40e_set_ringparam().

Fixes: be1222b5

 ("i40e: Separate kernel allocated rx_bi rings from AF_XDP rings")
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>