TS-2174: Fix traffic_shell broken by TS-1740

traffic_shell will show zero stats value in some fileds.

The root cause of this issue is that traffic_shell use RecFloat type to
read most stats variables, though these variables are no longer RecFloat
type after applied TS-1740, as a result bad conversion occurred.

We should make traffic_shell works as traffic_line, use the correct
conversion to read stats variables.

Signed-off-by: Yunkai Zhang <qiushu.zyk@taobao.com>