Remove Panic for unknown auth type

[JeremyRubin]

tokio-socks/src/tcp.rs

Line 425 in 9fdcccc

_ => unimplemented!(),

Panicking is not a great option here -- we should probably return an error instead.

[sticnarf]

The branch is unreachable. All unknown authentication method code will be matched by the m if m != self.auth.id() branch.

We can add a comment here and use unreachable! macro instead.

[JeremyRubin]

I see!

why not remove the if m != self.auth.id()?