Enable multiple connections with WinHttpHandler by default#2416

JamesNK merged 2 commits intogrpc:mastergrpc/grpc-dotnet:masterfrom

JamesNK:jamesnk/winhttphandler-usemultipleconnectionsJamesNK/grpc-dotnet:jamesnk/winhttphandler-usemultipleconnectionsCopy head branch name to clipboard