lstack: Streamline interface with TCON_CONTAINER

lstack: Streamline interface with TCON_CONTAINER

The interfaces the lstack module currently has implement (partial) type
safety in a somewhat clunk way - types and member names need to be passed
to a number of entry points.

This patch uses the new TCON_CONTAINER magic to stash the typing
information into the declaration of the stack object, so it no longer needs
to be explicitly passed to later calls.

This does alter the lstack interface incompatibly.  I think the module
is young enough that we can reasonably do that.  One other module,
'aga', was using lstack, and this also includes fixes so that it still
works.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>