[netdog] Improve error messaging in netdog when failing to match type of network device

[yeazelm]

There is a known issue in serde where matching enums obscures the errors when failing to match, making the user-facing errors opaque. Its been around for a while and folks have tried their own ways of solving this.

Since we have lots of exposure to this issue, we should figure out a way to expose the Deserialization failures to end users in a better way so they can debug why their net.toml isn't parsing into proper configuration. The primary goal is to provide the lower-level errors to the user so they can piece together why their config didn't result in proper configuration. Pulling this in will allow us to move all validation into Deserialize implementations and remove the Validate trait since our error messages won't be masked by the top-level enum deserialize.