ixgbe: optimize for XDP_REDIRECT in xsk path

ixgbe: optimize for XDP_REDIRECT in xsk path

Optimize ixgbe_run_xdp_zc() for the XDP program verdict being
XDP_REDIRECT in the xsk zero-copy path. This path is only used when
having AF_XDP zero-copy on and in that case most packets will be
directed to user space. This provides a little under 100k extra
packets in throughput on my server when running l2fwd in xdpsock.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Tested-by: Vishakha Jambekar <vishakha.jambekar@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>