dns: do not indicate invalid IPs are IPv6

In lib/dns.js, use `isIP()` instead of `isIPv4()` for determining the
`family` property in `lookup()`. If an invalid IP address is returned,
the `family` currently provided is `6`. With this change, it will be
`0`. Update documentation to reflect this.

doc/api/dns.md

@@ -154,7 +154,9 @@ changes:
 * `callback` {Function}
   - `err` {Error}
   - `address` {string} A string representation of an IPv4 or IPv6 address.
-  - `family` {integer} `4` or `6`, denoting the family of `address`.
+  - `family` {integer} `4` or `6`, denoting the family of `address`, or `0` if
+    the address is not an IPv4 or IPv6 address. `0` is a likely indicator of a
+    bug in the name resolution service used by the operating system.
 
 Resolves a hostname (e.g. `'nodejs.org'`) into the first found A (IPv4) or
 AAAA (IPv6) record. All `option` properties are optional. If `options` is an

lib/dns.js

@@ -23,7 +23,7 @@
 
 const cares = internalBinding('cares_wrap');
 const { toASCII } = require('internal/idna');
-const { isIP, isIPv4, isLegalPort } = require('internal/net');
+const { isIP, isLegalPort } = require('internal/net');
 const { customPromisifyArgs } = require('internal/util');
 const errors = require('internal/errors');
 const {
@@ -60,7 +60,7 @@ function onlookup(err, addresses) {
   if (this.family) {
     this.callback(null, addresses[0], this.family);
   } else {
-    this.callback(null, addresses[0], isIPv4(addresses[0]) ? 4 : 6);
+    this.callback(null, addresses[0], isIP(addresses[0]));
   }
 }
 
@@ -75,7 +75,7 @@ function onlookupall(err, addresses) {
     const addr = addresses[i];
     addresses[i] = {
       address: addr,
-      family: family || (isIPv4(addr) ? 4 : 6)
+      family: family || isIP(addr)
     };
   }