the current value of 256 limits the number of PDCP SDUs that can be
notified from RLC. The limit is quickly hit when too many SDUs
are in flight. This can cause unwanted log entries and weird PDCP
behaviour.
the patch increases the value to 1024, which still can be too few if
many smaller SDUs are traveling.
The patch also set the log level to warning to quicker spot
misconfigs in logs.
Fixes#2616