My first thought also was that the parts are used for mounting concertina/razor wire for barriers. However, thinking this over and after looking at the pics further I am thinking that isn't the case.
Although they look like they might be "field modifications" the design looks to me to be too complicated for wire mounting posts. IMHO, it would take a lot less extra work for someone in the motor pool to come up with a more simple design to hold wire. Plus, the area that houses these parts normally was the place to mount a spare tire.
Again, IMHO, I'd think that if I were the soldier driving the vehicle, I'd NOT sacrifice a spare wheel just for a place to store simple barrier wire mounts. I'd keep the tire and toss the wire mounting parts on top of the vehicle or tie them down somewhere.
With all this being said, I think there is a definite IMPORTANT purpose to these parts and I'm thinking they are some sort of armor; a modified anti-RPG "cage" perhaps? Maybe the "bad guys" were targeting the vehicle at the spare tire mount and it turned up being vulnerable? So, someone came up with these mounted parts to protect that area, without having to mount "birdcage" armor over the entire vehicle?
Just my WAG (Wild A** Guess)...