add some debugging info to assert

Original commit: elastic/x-pack-elasticsearch@ef3c68e4db

elasticsearch/x-pack/security/src/main/java/org/elasticsearch/xpack/security/transport/ServerTransportFilter.java

@@ -91,7 +91,7 @@ public interface ServerTransportFilter {
                 } else if (((TcpTransportChannel) unwrappedChannel).getChannel() instanceof io.netty.channel.Channel) {
                     io.netty.channel.Channel channel = (io.netty.channel.Channel) ((TcpTransportChannel) unwrappedChannel).getChannel();
                     io.netty.handler.ssl.SslHandler sslHandler = channel.pipeline().get(io.netty.handler.ssl.SslHandler.class);
-                    assert sslHandler != null;
+                    assert sslHandler != null : "channel [" + channel + "] did not have a ssl handler. pipeline " + channel.pipeline();
                     extactClientCertificates(sslHandler.engine(), channel);
                 }
             }