Description of problem:

connect to AF_UNSPEC to cancel an on-going connect does not work for AF_INET6 socket.

How reproducible:

Always

Steps to Reproduce:

```
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <assert.h>

static void* connect_socket(void* arg)
{
    int s = (int)(long)arg;

    struct sockaddr_in6 address;
    address.sin6_family = AF_INET6;
    inet_pton(AF_INET6, "::ffff:1.1.1.1", &address.sin6_addr);
    address.sin6_port = htons(23);

    int rv = connect(s, (struct sockaddr*)&address, sizeof(address));
    assert(rv != 0);

    return NULL;
}

int main()
{
    // create AF_INET6 socket
    int s = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);

    // on-going connect to 1.1.1.1:23
    pthread_t connect_thread;
    int rv = pthread_create(&connect_thread, NULL, connect_socket, (void*)(long)s);
    assert(rv == 0);
    sleep(1); // sleep to wait until connect is on-going.

    // connect to AF_UNSPEC
    struct sockaddr address;
    address.sa_family = AF_UNSPEC;
    rv = connect(s, &address, sizeof(address));

    // wait for thread
    rv = pthread_join(connect_thread, NULL);
    assert(rv == 0);

    return 0;
}

```

```
$ gcc main.c -lpthread
$ ./a.out
```

Actual results:

On RHEL7 this program hangs.
connect to AF_UNSPEC returns EINVAL.

Expected results:

On other Linux systems the program completes.
connect to AF_UNSPEC returns 0.
connect to AF_INET6 returns ECONNRESET.

Additional info:

This issue was discovered as part of .NET Core CI testing: https://github.com/dotnet/runtime/issues/42686.