i40e: fix xdp handle calculations

i40e: fix xdp handle calculations

Commit 4c5d9a7fa149 ("i40e: fix xdp handle calculations") reintroduced
the addition of the umem headroom to the xdp handle in the i40e_zca_free,
i40e_alloc_buffer_slow_zc and i40e_alloc_buffer_zc functions. However,
the headroom is already added to the handle in the function i40_run_xdp_zc.
This commit removes the latter addition and fixes the case where the
headroom is non-zero.

Fixes: 4c5d9a7fa149 ("i40e: fix xdp handle calculations")
Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>