@guruprasad I understand the frustration in trying to get your snap working under strict confinement, however for a snap to be granted the ability to use classic confinement, it must meet the requirements for classic confinement and fit into one of the supported categories for classic confinement as listed at Process for reviewing classic confinement snaps - can you please take a look at that page and update this thread with these details? If however the snap does not meet these requirements / fit within one of the supported categories then currently it is not possible to be granted classic confinement.
Unfortunately it is not possible for all applications to fit within the snap confinement model, however I hope that perhaps we can still work with you to help get your snap working under strict confinement (although it is hard without access to the particular hardware device). Also I am surprised by the snappy-debug output - that seems to indicate that the interface is not connected - can you check to make sure you have manually connected the various interfaces (as most do not auto-connect by default).