data race on ipv6_works

[bprodoehl]

I did this

I ran a multi-threaded app that uses libcurl under Clang 3.9 ThreadSanitizer.

I expected the following

Clean operation.

curl/libcurl version

7.44

operating system

Ubuntu 14.04, x86_64.

I encountered a data race with two threads calling Curl_ipv6works() at the same time. I think perhaps the call to Curl_ipv6works() should be moved into curl_global_init() to avoid this.

[bagder]

Sounds like an excellent suggestion to me. You up to providing such a change as a pull request?

[bprodoehl]

Sure thing. I should be able to put that together and test it tonight.

[jay]

Thanks, landed in c509808.