[ruby/net-smtp] Add SNI support to net/smtp

https://github.com/ruby/net-smtp/commit/b706942392

lib/net/smtp.rb

@@ -600,6 +600,7 @@ module Net
       s = ssl_socket(s, @ssl_context)
       logging "TLS connection started"
       s.sync_close = true
+      s.hostname = @address if s.respond_to? :hostname=
       ssl_socket_connect(s, @open_timeout)
       if @ssl_context.verify_mode && @ssl_context.verify_mode != OpenSSL::SSL::VERIFY_NONE
         s.post_connection_check(@address)