webadmin: change the length tooltip of QoS's name

The length tooltip of QoS's name is not correct now. The length of
name field in the database(network_qos table) is 50. But the tooltip
tells the length is 255.

This patch fix the problem. It modify the tooltip, make it to show the
correct message (i.e. under 50 characters).

Change-Id: Ic9cb4e40dfc213016a819866baccba40529bd270
Bug-Url: https://bugzilla.redhat.com/1105010
Signed-off-by: Ma Like <like.ma@cs2c.com.cn>