ares: remove fd from multi fd set when ares is about to close the fd

When using c-ares for asyn dns, the dns socket fd was silently closed
by c-ares without curl being aware. curl would then 'realize' the fd
has been removed at next call of Curl_resolver_getsock, and only then
notify the CURLMOPT_SOCKETFUNCTION to remove fd from its poll set with
CURL_POLL_REMOVE. At this point the fd is already closed.

By using ares socket state callback (ARES_OPT_SOCK_STATE_CB), this
patch allows curl to be notified that the fd is not longer needed
for neither for write nor read. At this point by calling
Curl_multi_closed we are able to notify multi with CURL_POLL_REMOVE
before the fd is actually closed by ares.

In asyn-ares.c Curl_resolver_duphandle we can't use ares_dup anymore
since it does not allow passing a different sock_state_cb_data

Closes #3238

lib/multiif.h

@@ -89,7 +89,7 @@ void Curl_multi_connchanged(struct Curl_multi *multi);
  * socket again and it gets the same file descriptor number.
  */
 
-void Curl_multi_closed(struct connectdata *conn, curl_socket_t s);
+void Curl_multi_closed(struct Curl_easy *data, curl_socket_t s);
 
 /*
  * Add a handle and move it into PERFORM state at once. For pushed streams.