Remote DFS root support.

Allows to mount share on a server that returns -EREMOTE
 at the tree connect stage or at the check on a full path
 accessibility.

Signed-off-by: Igor Mammedov <niallain@gmail.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>