androiddump: Fix non-blocking connect on Windows

Commit 043ed1f6 enabled non-blocking connect on Windows. This seems to
break androiddump on Windows completely, since a successful connection
always returns SOCKET_ERROR on connect, with WSAGetLastError() set to
WSAEWOULDBLOCK.

Apparently, the only way to check for a real connection is to try a
write select on the socket:
https://stackoverflow.com/questions/35370239/timeout-in-connect-function-from-winsock

This fixes androiddump on Windows:
- If ADB server is running, extcap interfaces are listed
- If ADB is not running, there is no noticeable delay in Wireshark

Change-Id: I6bd772215c7b232c8fe8e840cb7ad1d54c7d8860
Reviewed-on: https://code.wireshark.org/review/25715
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

extcap/androiddump.c

@@ -547,6 +547,22 @@ static socket_handle_t adb_connect(const char *server_ip, unsigned short *server
     while (tries < SOCKET_CONNECT_TIMEOUT_TRIES) {
         status = connect(sock, (struct sockaddr *) &server, (socklen_t)sizeof(server));
         tries += 1;
+
+#ifdef _WIN32
+        if ((status == SOCKET_ERROR) && (WSAGetLastError() == WSAEWOULDBLOCK)) {
+            const struct timeval timeout = {
+                .tv_sec = 0,
+                .tv_usec = SOCKET_CONNECT_DELAY_US,
+            };
+            fd_set fdset;
+            FD_ZERO(&fdset);
+            FD_SET(sock, &fdset);
+            if ((select(0, NULL, &fdset, NULL, &timeout) != 0) && (FD_ISSET(sock, &fdset))) {
+                status = 0;
+            }
+        }
+#endif
+
         if (status != SOCKET_ERROR)
             break;
         g_usleep(SOCKET_CONNECT_DELAY_US);