- pcap_open did not return NULL if fopen failed
- libfreerdp-core, tfreerdp-serer and xfreerdp-server did not check the pcap_open result
- also fixed the sleep calculation in the xfreerdp-server
pcap used utils/stopwatch to save a record's timestamp which is not suitable because stopwatch measures cpu time and not the wall-clock time
also fixed the sleep calculation in the tfreerdp test server