sync header with lttng-tools

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
babeltrace handle the inactive streams (review needed)

when content_size == 0, just set the timestamp_end of the packet and
reinsert the stream in the heap.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
handle inactive beacons

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>