Build snifftest on Windows

To build the snifftest executable on Windows, first follow the steps to build wolfSSL on Visual Studio found here.
Next, download the WinPcap development pack found here.
Extract the WpdPack folder from the downloaded zip and place adjacently to the wolfSSL directory as shown below.
```
  Projects\
      wolfssl\
      WpdPack\
```
Then on Visual Studio, open the configuration manager for the wolfssl solution. This can be done by right-clicking on the solution viewer then selecting properties. The button for the configuration manager should be on the top-right of the window.
On the configuration manager, tick the box to build sslSniffTest on your desired configuration. Make sure to configure the project for either Release or Debug and not DLL Release or DLL Debug. The snifftest project requires sslSniffer.lib, which is not built in the cases of DLL Release and DLL Debug.
Add the following to your user_settings.h.

#define WOLFSSL_STATIC_EPHEMERAL
#define WOLFSSL_DH_EXTRA
#define HAVE_ECC
#define HAVE_ECC_SECPR2

For details on usage, see sniffer README.md for more details.