This commit fix current QU bit implementation that may be used in mDNS
protocol. Indeed, until now, if a packet with QU bit set is received,
it is decoded as:

{

  ...

  questions: [
    {
      name: '...',
      type: 'PTR',
      class: 'UNKNOWN_32769'
    },
    {
      name: '...',
      type: 'PTR',
      class: 'UNKNOWN_32769'
    }
  ],

  ...

}

Instead of :

{

  ...

  questions: [
    {
      name: '...',
      type: 'PTR',
      class: 'IN'
    },
    {
      name: '...',
      type: 'PTR',
      class: 'IN'
    }
  ],

  ...

}

This commit adds a proper QU bit support via the qu_bit field.
It enables:

- The encoder to parse properly both the class and the QU bit
- THe decoder to encode a DNS packet with the QU bit set

This commit includes several fixes that addess lint issues introduced by
commit a7a0b78

The code using this constant was removed by the commit
a7a0b78