don't log all the cancelled context errs (they are expected as we sen…

…d in the bg)

mixing/mixclient/client.go

@@ -1754,7 +1754,7 @@ func (c *Client) roots(ctx context.Context, seenSRs []chainhash.Hash,
 			err := c.sendLocalPeerMsgs(ctx, sesRun, func(p *peer) mixing.Message {
 				return p.fp
 			})
-			if err != nil {
+			if ctx.Err() == nil && err != nil {
 				c.logf("%v", err)
 			}
 			publishedRoots <- struct{}{}