Lets Begins.
For this purposes, there are some few thing need to be done.
1. Upgrade the App Service Plan to Standard or Premium
2. Connection to Arcsight Syslog NG ; vNet peering- Within Azure , S2S VPN - Outside Azure
3. Congfigure the vNet Integration
4. Change the connection to Arcsight Syslog NG from its Public IP to Private IP.
* Even thought it gone through Public IP , its was on TLS .
Do not Forget to restart both Function after this setting has been applied and walla you are done.