[HACKERS] foreign table creation and NOT VALID check constraints

In f27a6b15e656 (9.6 & later), we decided to "Mark CHECK constraints
declared NOT VALID valid if created with table."  In retrospect,
constraints on foreign tables should have been excluded from consideration
in that commit, because the thinking behind the aforementioned commit
(that the constraint is trivially validated because the newly created
table contains no data) does not equally apply to the foreign tables case.

Should we do something about that?

Thanks,
Amit