sockets: change inet_connect() to support nonblock socket

Add a bool argument to inet_connect() to assign if set socket
to block/nonblock, and delete original argument 'socktype'
that is unused.
Add a new argument to inet_connect()/inet_connect_opts(),
to pass back connect error by error class.

Retry to connect when -EINTR is got. Connect's successful
for nonblock socket when following errors are got, user
should wait for connecting by select():
  -EINPROGRESS
  -EWOULDBLOCK (win32)
  -WSAEALREADY (win32)

Change nbd, vnc to use new interface.

Signed-off-by: Amos Kong <akong@redhat.com>
Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/qemu-char.c b/qemu-char.c
index a9fc504..060bf9d 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2446,7 +2446,7 @@
         if (is_listen) {
             fd = inet_listen_opts(opts, 0);
         } else {
-            fd = inet_connect_opts(opts);
+            fd = inet_connect_opts(opts, NULL);
         }
     }
     if (fd < 0) {