Documentation/connector/cn_test.c comment unused cn_test_want_notify()

Currently cn_test_want_notify() has no user.

So add an ifdef and a comment which tells us to not remove it.

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>