This big patch fixes fragmentation handling in the dynamic channel. We used to
have a single state to handle fragmentation at the main dynamic channel level, but
in fact packets can be fragmented per sub channel. So we have to maintain a fragmentation
state per sub channel, this involve treating dynamic and static channels differentely
(so the size of the patch that has to implement state tracking per dynamic channels).
The rework introduce a stateful dynamic channel treatment, so that we can take early decisions
for data packet (dropping all the current packet or pass it), but also reassemble important
packets like channel creation.
