dns: cleanup validation

The `validateString()` validator should cleanup the validation and
keep consistency.

Author: VoltrexKeyva

lib/internal/dns/utils.js

@@ -131,9 +131,8 @@ class Resolver {
   setLocalAddress(ipv4, ipv6) {
     validateString(ipv4, 'ipv4');
 
-    if (typeof ipv6 !== 'string' && ipv6 !== undefined) {
-      throw new ERR_INVALID_ARG_TYPE('ipv6', ['String', 'undefined'], ipv6);
-    }
+    if (ipv6 !== undefined)
+      validateString(ipv6, 'ipv6');
 
     this._handle.setLocalAddress(ipv4, ipv6);
   }