Avoid warning "comparison of unsigned expression < 0 is always false"

lib/hostip6.c

@@ -238,7 +238,7 @@ Curl_addrinfo *Curl_getaddrinfo(struct connectdata *conn,
 
   /* see if we have an IPv6 stack */
   s = socket(PF_INET6, SOCK_DGRAM, 0);
-  if (s < 0) {
+  if (s != CURL_SOCKET_BAD) {
     /* Some non-IPv6 stacks have been found to make very slow name resolves
      * when PF_UNSPEC is used, so thus we switch to a mere PF_INET lookup if
      * the stack seems to be a non-ipv6 one. */