Traversal: update pending-packet time on socket timeout

Pending traversal packets were only expired after receive events. If a
client did not acknowledge a response and no more packets arrived, the
server retained the pending entry indefinitely.

Update the current time before handling socket timeouts. Pending packets
will then retry and expire while the server is idle.

Source/Core/Common/TraversalServer.cpp

@@ -470,6 +470,9 @@ int main()
     FD_SET(sock, &readSet);
     FD_SET(sockAlt, &readSet);
     rv = select(std::max(sock, sockAlt) + 1, &readSet, nullptr, nullptr, &tv);
+    currentTime = std::chrono::duration_cast<std::chrono::microseconds>(
+                      std::chrono::steady_clock::now().time_since_epoch())
+                      .count();
     if (rv < 0)
     {
       if (errno != EINTR && errno != EAGAIN)
@@ -499,9 +502,6 @@ int main()
     // note: switch to recvmmsg (yes, mmsg) if this becomes
     // expensive
     rv = recvfrom(recvsock, &packet, sizeof(packet), 0, (sockaddr*)&raddr, &addrLen);
-    currentTime = std::chrono::duration_cast<std::chrono::microseconds>(
-                      std::chrono::system_clock::now().time_since_epoch())
-                      .count();
     if (rv < 0)
     {
       if (errno != EINTR && errno != EAGAIN)