ixgbe: Fix possible skb NULL pointer dereference

The commit c824125c ("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: c824125c ("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>