ovn-controller: Rename init functions that just register IDL columns.

ovn-controller: Rename init functions that just register IDL columns.

The generic *_init() names for these functions made it sounds like they
do something more than just register IDL columns, even though that's all
they do.  Also, the controller_ctx that was passed into each of them was
only used to get the IDL handle.  This commit renames them and changes
their parameter type to simplify and make all of this clearer.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Justin Pettit <jpettit@nicira.com>