cope with openbsd nonstandard bpf_timeval

Index: src/NetworkInterface.cpp
--- src/NetworkInterface.cpp.orig
+++ src/NetworkInterface.cpp
@@ -1997,9 +1997,13 @@ bool NetworkInterface::processPacket(u_int32_t bridge_
      (2) ensures that periodic_stats_update is not performed too frequently as it could be detrimental for performances and lead
          to packet drops.
    */
+  timeval tmpt;
+  tmpt.tv_sec = when->tv_sec;
+  tmpt.tv_usec = when->tv_usec;
+
   if(flow->get_current_bytes_cli2srv() + flow->get_current_bytes_srv2cli() >= PERIODIC_STATS_UPDATE_MIN_REFRESH_BYTES
-     && Utils::msTimevalDiff(when, flow->get_current_update_time()) >= PERIODIC_STATS_UPDATE_MIN_REFRESH_MS) {
-    flow->periodic_stats_update(when);
+     && Utils::msTimevalDiff(&tmpt, flow->get_current_update_time()) >= PERIODIC_STATS_UPDATE_MIN_REFRESH_MS) {
+    flow->periodic_stats_update(&tmpt);
   }
 
   return(pass_verdict);