ixgbe: use return codes from ndo_xdp_xmit that are distinguishable

For XDP_REDIRECT the use of return code -EINVAL is confusing, as it is
used in three different cases.  (1) When the index or ifindex lookup
fails, and in the ixgbe driver (2) when link is down and (3) when XDP
have not been enabled.

The return code can be picked up by the tracepoint xdp:xdp_redirect
for diagnosing why XDP_REDIRECT isn't working.  Thus, there is a need
different return codes to tell the issues apart.

I'm considering using a specific err-code scheme for XDP_REDIRECT
instead of using these errno codes.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>