ttcn3-tcpdump-stop.sh: Wait to receive last packets before stopping tcpdump

There's a time delay between packets are sent through the system and
tcpdump reads, buffers and stores them into the pcap file. We need to
give it more time to process everything before killing it, otherwise
last (or all) packets from the test are not captured.

Change-Id: I240d8f1bdb2ca6ad353e60ef15937dc2bd4cbebd
1 file changed