Feature request: dual mode operation

[M0LTE]

It would be really nice if tncattach could handle IP frames itself, as it does now, but anything non-IP gets passed through to a TCP socket so another application (e.g. BPQ32) could handle it. Any KISS frame received to that socket from another application would just get passed to the TNC and transmitted.

This way, a node could support dual mode operation - IP and "traditional" AX.25 at the same time - which might promote uptake.