Sorry I don't have an answer, just posting to say I'm curious about this as well.
I went so far as to build the character in Hero Lab, and it gives the mount the "Combat Trained" trick package, but then pops up a validation error saying "Too Many Tricks (6 of 4)". The other part of this is probably more a Hero Lab issue, but it won't allow me to remove any of the tricks to fit within the limit.
My guess is that either they thought the constrictor had 2 Int or that it is treated as int 2 just for starting with those tricks. The problem then becomes what to do if you increase its Int, or when it gets more bonus tricks from leveling.
Here's hoping we can get some kind of answer, or at least a consensus.