Call the callbacks with Fixnum values

[jonasschneider]

Just a reminder to do this someday: Currently, many of the callback arguments are read directly from BinData records and are therefore of class BinData::Bit31 or something. They behave like Fixnums, but become a problem when used as the key of a Hash, i.e.:

h = {}
h[pckt.header.stream_id] = 'foo'
pckt.header.stream_id == 1 # => true
h[1] => nil

Raw Fixnums should be used there.