request handler extension needed to transfer the ONU SW upgrade requests to openonu-adapter

With the implemtation of the new voltctl commands it is required to ensure the transfer of the request with all required/optional arguments to the openonu adapter.

In the current implementation such requests ends up in some panic, e.g.:

{"level":"debug","ts":"2021-01-12T08:59:00.848Z","caller":"kafka/sarama_client.go:947","msg":"message-received","instanceId":"open-onu-voltha-adapter-openonu-79b44494c7-6j67x","timestamp":"1754-08-30T22:43:41.128Z","receivedTopic":"minimal-brcm_openomci_onu"} {"level":"debug","ts":"2021-01-12T08:59:00.848Z","caller":"kafka/kafka_inter_container_library.go:882","msg":"received-request","instanceId":"open-onu-voltha-adapter-openonu-79b44494c7-6j67x","op-id":"678d8a8daffd49c9","op-name":"/voltha.VolthaService/DownloadImage","task-id":"17b132b9b35c5963","task-name":"kafka-rpc-download_image","device-id":"f00bb32c-762e-4d6d-9720-5733c5ebf014","rpc":"download_image","header":"id:\"37ce18dd-ef8a-40f4-8bcc-5477d5647d6c\" from_topic:\"minimal-rwcore\" to_topic:\"minimal-brcm_openomci_onu\" key_topic:\"f00bb32c-762e-4d6d-9720-5733c5ebf014\" timestamp:<seconds:1610441940 nanos:844580961 > "}

panic: reflect: Call with too many input arguments

Andrea already proposed some solution for request_handler lines 562..564 similar to

https://github.com/opencord/voltha-lib-go/blob/46a9f01ade07e5772e1cf1ac61779de89564f734/pkg/adapters/common/request_handler.go#L106-L141

Or compare py solution: https://gerrit.opencord.org/c/pyvoltha/+/19479.