[Patch] Add support for lattice element free

[Jun Xiao]

This is very useful to cleanup memory after pt_loop done.

Thanks,

Jun

[Jun Xiao]

Please ignore the previous patch which doesn't deal with lattice with load balance routers.

This patch add more things:

- reference count for mda_interface_t, so the interface can be deferred to free until no reference.

- lattice element will be conditionally freed depending on user data (i.e. mda_interface_t) is ready to free or not

- some misc fixes on memory leak on corner cases.

Thanks,

Jun

[Jun Xiao]

Forgot the attachment.