Um, skip 0 tests?

When we call `skip(1, ...)`, we get output like this:
```
7: Test timeout computed to be: 1500
7: 1..1
7: ok 1 # skip DISABLE_IPV6_TESTS
7: ok 2 - NdbGetInAddr
7: # 1 tests planned but 2 executed
1/1 Test mysql#7: NdbGetInAddr-t ...................***Failed    0.00 sec

0% tests passed, 1 tests failed out of 1
```

That is, the test suite thinks we ran more tests than we planned, which is
its own failure.  `skip(0, ...)` doesn't actually print the message or say
anything was skipped, but it results in a passing message:

```
7: Test command: /home/patrick/src/mysql-server/build/runtime_output_directory/NdbGetInAddr-t
7: Test timeout computed to be: 1500
7: 1..1
7: ok 1 - NdbGetInAddr
1/1 Test mysql#7: NdbGetInAddr-t ...................   Passed    0.00 sec
```

For posterity, here is the command to run just that one test:

```bash
DISABLE_IPV6_TESTS=1 DISABLE_TMPFILE_TESTS=1 make test ARGS="-R ^NdbGetIn -VV"
```

Author: piki

storage/ndb/src/common/portlib/NdbTCP.cpp

@@ -500,7 +500,7 @@ TAPTEST(NdbGetInAddr)
 {
   if (getenv("DISABLE_IPV6_TESTS")) {
     // fails when ipv6 is present but disabled
-    skip(1, "DISABLE_IPV6_TESTS");
+    skip(0, "DISABLE_IPV6_TESTS");
     return 1;
   }