xdp: fix possible cq entry leak

xdp: fix possible cq entry leak

Completion queue address reservation could not be undone.
In case of bad 'queue_id' or skb allocation failure, reserved entry
will be leaked reducing the total capacity of completion queue.

Fix that by moving reservation to the point where failure is not
possible. Additionally, 'queue_id' checking moved out from the loop
since there is no point to check it there.

Fixes: 35fcde7f8deb ("xsk: support for Tx")
Signed-off-by: Ilya Maximets <[email protected]>
Acked-by: Björn Töpel <[email protected]>
Tested-by: William Tu <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>