ISDN:divert: beautify code: useless 'break', 'return (0)', additional comments.

  delete useless 'break' after 'return'.
  let 'return 0' instead of 'return (0)'
  also give a comment for 'break' to let readers notice it.

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>