tcp: warn on negative reordering values

tcp: warn on negative reordering values

Commit bafbb9c73241 ("tcp: eliminate negative reordering
in tcp_clean_rtx_queue") fixes an issue for negative
reordering metrics.

To be resilient to such errors, warn and return
when a negative metric is passed to tcp_update_reordering().

Signed-off-by: Soheil Hassas Yeganeh <[email protected]>
Signed-off-by: Neal Cardwell <[email protected]>
Signed-off-by: Yuchung Cheng <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>