Ignore non-port related messages in native compactor driver

The view native compactor driver process needs to handle only
Port related messages. It can ignore receiving any messages
such as pause message sent by unit test.

Change-Id: Iafd4f15219933f37a28d618db79ea95bbad5b5e9
Reviewed-on: http://review.couchbase.org/33161
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>