Ignore all but delta messages
Ignore all but delta messages

A provider, especially a provider piping data from
another Signal K server, may produce stuff we don't
understand, so handle only delta messages.

SignalK/signalk-server-node,sbender9/signalk-server-node,sbender9/signalk-server-node,webmasterkai/signalk-server-node,webmasterkai/signalk-server-node,SignalK/signalk-server-node,SignalK/signalk-server-node,SignalK/signalk-server-node,webmasterkai/signalk-server-node,sbender9/signalk-server-node