The "no space is necessary after a cast" sizeof exclusion doesn't work
properly.

The test reports a false positive for code like:

	BUILD_BUG_ON(sizeof(struct batadv_bla_claim_dst) != 6);

Make it work, simplify the exclusions, and add some comments.
Signed-off-by: NJoe Perches <joe@perches.com>
Reported-by: NMarek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>