pktdumper: Use usleep instead of sleep

MinGW doesn't have sleep, only _sleep (which is deprecated),
Sleep (which is defined in winbase.h and not in the standard
C headers) and usleep.

Signed-off-by: Martin Storsjö <martin@martin.st>

tools/pktdumper.c

@@ -120,7 +120,7 @@ int main(int argc, char **argv)
     avformat_close_input(&fctx);
 
     while (donotquit)
-        sleep(60);
+        usleep(60 * 1000000);
 
     return 0;
 }