Hmm. Well, I've searched the forum, and the general consensus is that strictly speaking, garlic is a no-no - because of the whole 'it may kick you out of ketosis', 'might give you the munchies' thing.
But there's a lot of anecdotal stuff along the lines of, 'I've always used a tiny bit and it's been fine' too.
I think it's one of those 'tweak the diet at your own risk' decisions. The problem with tweaking for some of us is that it can feel a bit like cheating - and feeling as though we've cheated can do funny things to our heads and set us off on binges.
But if you're not one of those people and the thought of having a smidgeon of garlic is driving you crazy, I suspect that you might get away with having a little tiny bit. I cannot imagine that the amount of carbs in a little bit would kick you out of ketosis.