lib: create_packet_message(): make assertion message less convoluted

Instead of having a message which enumerated the possible precondition
breaks, have it say that the stream class has an unexpected configuration,
and add the "packets have default beginning clock snapshot" and
"packets have default end clock snapshot" properties to the extended
logging of a stream class object in `lib-logging.c`.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Ic7b706b9d6ef3afb799072a8891a0ba24370f317
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1364
Tested-by: jenkins
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>