Buffs Bulldog shotgun stun time

After seeing a few nuke op teams fail because of this (and being part of one of them), I feel that the Bulldog is almost useless now. It takes two shots to down someone, and they almost immediately pop right back up because of the high stamina recovery rate. Generally this makes it fail in combat unless your target is ill-prepared, and it's completely useless against crowds.

This PR attempts to fix that. Instead of taking two shots, stun rounds now take one hit to knock down the target and also do additional stamina damage. Because of the high stamina recovery rate, the stun generally doesn't last long in the first place. By making it a single-shot stun, the Bulldog assumes its original usability and makes it friendlier to stealth ops.