ovsdb-idl: Improve ovsdb_idl_add_table() comment.
The new comment reflects with more clarity what ovsdb_idl_add_table() does.
Previous comment could be misunderstood, leading to believe that this function
replicates all columns on IDL. Hopefully this fix clarifies that columns are
not replicated, just minimal data for reference integrity is replicated.
A comment in ovsdb_idl_table_class is also modified to better reflect this
behaviour.
Signed-off-by: Edward Aymerich <edward.aymerich@hpe.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>