ipset creation error parsing seems broken

[bleggett]

1. Manually create an ipset named my-special-ipset

2. Run the following code:

	err := netlink.IpsetCreate("my-special-ipset, "hash:ip", netlink.IpsetCreateOptions{Comments: true, Replace: true, Family: family})
	log.Debugf("IPSET ERROR IS: %s", err)
	if err == nl.IPSetError(nl.IPSET_ERR_EXIST) {
 		return nil
 	}

3. does NOT return nil, as you would expect.
4. debug log outputs IPSET ERROR IS: file exists

[bleggett]

I suspect this is the result of an early return that basically skips error mapping:

netlink/ipset_linux.go

Line 410 in d13535d

msgs, err = req.Execute(unix.NETLINK_NETFILTER, 0)