eventscripts: Tweak the timeout check in kill_tcp_connections()

eventscripts: Tweak the timeout check in kill_tcp_connections()

This has 2 advantages:

1. It uses get_tcp_connections_for_ip() to check for leftover
   connections, instead of custom code.

2. It checks for the timeout condition before sleeping.  The current
   code sleeps and then checks, so wastes a second.

Signed-off-by: Martin Schwenke <martin@meltin.net>