modules: make MODULE_IMPORT_NS() work even when modular builds are disabled

It's an unusual configuration, and was apparently never tested, and not
caught in linux-next because of a combination of travels and it making
it into the tree too late.

The fix is to simply move the #define to outside the CONFIG_MODULE
section, since MODULE_INFO() will do the right thing.

Cc: Martijn Coenen <maco@android.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matthias Maennich <maennich@google.com>
Cc: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>