controller: Add `converged` flag to level iterator.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
controller: Add `bind_if_not_converged` macro.

Signed-off-by: Matthew Emmett <memmett@gmail.com>
mlsdc: Use bind_if_not_converged in favour of exceptions.

Signed-off-by: Matthew Emmett <memmett@gmail.com>