EarlyNetworkSetupError: stop duplicate log output on DnsResolver variant

Similar to the last commit, this updates the #[error(...)] attribute on
the DnsResolver variant on EarlyNetworkSetupError, to avoid recursing
into the Display implementation of ResolveError.

All callers appear to be handling EarlyNetworkSetupError correctly
already, so this commit doesn't make any other changes.

Author: sruggier

sled-agent/src/bootstrap/early_networking.rs

@@ -71,7 +71,7 @@ pub enum EarlyNetworkSetupError {
     #[error("Error during request to Dendrite: {0}")]
     Dendrite(String),
 
-    #[error("Error during DNS lookup: {0}")]
+    #[error("Error during DNS lookup")]
     DnsResolver(#[from] ResolveError),
 
     #[error("BGP configuration error: {0}")]