[flang] Fix bug with host-association in module procedure interface body

A module procedure interface body can access entities in its host
without an IMPORT statement. So the `ImportKind` of the scope created
for such an interface body should be `Default`, not `None` as it is
for other interface bodies.

Original-commit: flang-compiler/f18@24bb2668fdb626a4df76719345b02e533d015d79
Reviewed-on: https://github.com/flang-compiler/f18/pull/305
Tree-same-pre-rewrite: false