net: export isIPv4, isIPv6 directly from cares

The function objects encapsulating `isIPv4` and `isIPv6` are not
necessary. They can be directly exposed from `cares`.

PR-URL: #7481
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/net.js

@@ -1581,14 +1581,10 @@ Server.prototype.unref = function() {
 exports.isIP = cares.isIP;
 
 
-exports.isIPv4 = function(input) {
-  return cares.isIPv4(input);
-};
+exports.isIPv4 = cares.isIPv4;
 
 
-exports.isIPv6 = function(input) {
-  return cares.isIPv6(input);
-};
+exports.isIPv6 = cares.isIPv6;
 
 
 if (process.platform === 'win32') {