sendrecv: make them two pairs of send/recv to properly deal with FTPS

FTP(S) use two connections that can be set to different recv and
send functions independently, so by introducing recv+send pairs
in the same manner we already have sockets/connections we can
work with FTPS fine.

This commit fixes the FTPS regression introduced in change d64bd82.

lib/qssl.c

@@ -268,8 +268,8 @@ CURLcode Curl_qsossl_connect(struct connectdata * conn, int sockindex)
   }
   if (rc == CURLE_OK) {
     connssl->state = ssl_connection_complete;
-    conn->recv = qsossl_recv;
-    conn->send = qsossl_send;
+    conn->recv[sockindex] = qsossl_recv;
+    conn->send[sockindex] = qsossl_send;
   }
 
   return rc;