HI
I run a large herd of Meat goats based on the Boer.
From a personal point of view you should consider a lot of things before you make rash decisions on this male. Importantly - why are you breeding boers, is it for perfect boers or is it for meat goats? Perfect Boers will need you be harsher on the kids than comercially viable meat goats would.
The BBGS does not automatically exclude certain multiple teat formations and you should do as suggested already - see the breed standard booklets for pictures of acceptable teats if you are hopeing to register the kids.
However as a rule of thumb, we personally take an objective view of the teats and work out if the extras are going to affect suckling, if the answer is no then we do not consider them to be a cull fault (but remeber that we are a meat herd and are making choices for that use)
I can also say that whilst teats must be hereditary in some ways - it appears to me to be fairly random- We have bred from more than 10 Boer Bucks now, some with 2 teats and some with extras and the kids seem to come out random from either.
IF you choose to select only for the number of teats then you MUST NOT loose sight of the carcass conformation. It is all too easy to get hung up on 1 aspect of the goat and find yourself in a mess later down the line when all your goats have a different issue you had not noticed arriving. eg week pasterns or poor legs etc.
Make sure you always look at the bigger picture and if this male throws the best carcasses then don't disregard him for future breeding for having the wrong number of teats, just be aware of it and make sure that you put him only to the does with the teats you are most pleased with.
After all this is the essence of all breeding - put animals with complementary traits together and then only keep the ones which have taken the traits you desitred and remove those which have taken both the bad bits
Good luck with your breeding - Enjoy owning Boers they are a wonderful breed to have around.