If you are referring to the keepalive functionality (see
https://github.com/grpc/grpc/blob/master/doc/keepalive.md), it can be configured for C# even without being explicitly exposed in the API.
What you need to do it to set the channel arguments (= ChannelOptions in the C# API) according to the documentation, e.g. new ChannelOption("the_string_name", value)
You can pass the channel options when creating a channel ("new Channel(target, channelOptions)" and when creating a server "new Server(channelOptions)".