netlink_listener_test deflake - again...

Reduce to 32500 sockets, since ulimit is set to 32768 open fds.

While at it fix up some comments, and do an earlier abort (but still fail)
to ease debugging if opening of sockets fails.
(otherwise you get tens of thousands of expect failures)

Test: built, ran atest
Bug: 144135648
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I5244953c553ac46432af80010e7acb9414926afd