Patch suggestion for wireshark's LAPDm dissector

Hello, (my first post to this ML) Sylvain told me it might be a good place to post this. Please find attached a small patch for wireshark's LAPDm dissector. It currently fails at reassembling LAPDm packets when processing multiple streams at the same time insofar as it always assume the fragmented type I LAPDm frames belong to the same stream. This is of course wrong if you process, for instance, all the timeslots of a S{D,A}CCH channel. The proposed patch, which might not be ideal but seems to work better with my testcase (and not worse), identifies the stream using the tuple (link direction, timeslot, subslot). I reused the packet_info's circuit_id field for this, which should be safe enough to use. Let me know if you have any comments., hopefully this could be committed upstream by someone with commit access. Best Regards, iZsh