You can't perform a silent installation of WinPcap because the company removed this feature from the installation package. However, there is a form of a silent installation available for WinPcap Pro, but since the package is almost 4000 $, it has no meaning to purchase it just for this feature.
If you use WinPcap from Wireshark, for example, you can append /S to the installation and it will install properly.
