llgs-tests: Increase packet time out

The default packet timeout of 1 second is a bit too small for these
tests, particularly as they are working in ack-mode, which means they
need to fit twice as many packets into the timeslot.

This does not seem to be a problem on the bots, but for some people
these tests are timing out regularly. I can't be sure increasing this
will solve their problem, but this does seem like a likely culprit.

llvm-svn: 330578