test: handle EUNATCH on IBM i

When IPv6 is disabled IBM i returns EUNATCH (errno 42).
For now, I've added an errno check in test case.
libuv needs to get updated to handle EUNATCH so that
the error code can be addressed as EUNATCH.

This change is related to changes done in
nodejs#46546

At the time this test case was not enabled

test/parallel/test-net-autoselectfamily-commandline-option.js

@@ -85,6 +85,10 @@ function createDnsServer(ipv6Addr, ipv4Addr, cb) {
         if (common.hasIPv6) {
           assert.strictEqual(error.code, 'ECONNREFUSED');
           assert.strictEqual(error.message, `connect ECONNREFUSED ::1:${port}`);
+        } else if (common.isIBMi) {
+          // IBMi returns EUNATCH (ERRNO 42) when IPv6 is disabled
+          // keep this errno assertion until EUNATCH is recognized by libuv
+          assert.strictEqual(error.errno, -42);
         } else {
           assert.strictEqual(error.code, 'EADDRNOTAVAIL');
           assert.strictEqual(error.message, `connect EADDRNOTAVAIL ::1:${port} - Local (:::0)`);