T6028: Fix QoS policy shaper wrong class_id_max and default_minor_id

The class_id_max is wrong due to tmp.sort of Strings
If we have class 5 and class 10 we get sorted max value 5, expected 10

>>> tmp = ['5', '10']
>>> tmp.sort()
>>> tmp
['10', '5']
>>>

>>> hex(5+1)
'0x6'
>>>
>>> hex(10+1)
'0xb'
>>>

This way we get wrong default maximum class value:

tc qdisc replace dev eth1 root handle 1: htb r2q 444 default 6

Expect:

tc qdisc replace dev eth1 root handle 1: htb r2q 444 default b

Fix this converting Strings to Integers and get max value.