ixgbe: Fix possible skb NULL pointer dereference

The commit c824125 ("ixgbe: Fix passing 0 to ERR_PTR in
ixgbe_run_xdp()") stopped utilizing the ERR-like macros for xdp status
encoding. Propagate this logic to the ixgbe_put_rx_buffer().

The commit also relaxed the skb NULL pointer check - caught by Smatch.
Restore this check.

Fixes: c824125 ("ixgbe: Fix passing 0 to ERR_PTR in ixgbe_run_xdp()")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/intel-wired-lan/2c7d6c31-192a-4047-bd90-9566d0e14cc0@stanley.mountain/
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Piotr Kwapulinski <piotr.kwapulinski@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Saritha Sanigani <sarithax.sanigani@intel.com> (A Contingent Worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Author: pkwapuli

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -2105,7 +2105,7 @@ static void ixgbe_put_rx_buffer(struct ixgbe_ring *rx_ring,
 		/* hand second half of page back to the ring */
 		ixgbe_reuse_rx_page(rx_ring, rx_buffer);
 	} else {
-		if (!IS_ERR(skb) && IXGBE_CB(skb)->dma == rx_buffer->dma) {
+		if (skb && IXGBE_CB(skb)->dma == rx_buffer->dma) {
 			/* the page has been released from the ring */
 			IXGBE_CB(skb)->page_released = true;
 		} else {