There's no AoOs in 1e...
While it is true that there are no things called AoO in 1e, there are rules scattered all over the place that act very much like AoOs. The one that comes most immediately to mind, is that if you attempt to flee from melee, your opponent is entitled to a free attack (on your back no less) before you disengage.
As for how I mostly see situations like this dealt with, the answer is generally:
All Editions) The PC's use their vastly superior ranged weapon attacks to pick off the Kobolds from atop the wall. This could include any of the following:
a) Just send a fireball to explode on the other side of the battlements, killing everything. Alternately, particularly at lower levels, they just cast sleep, suppressing all the kobolds with their pitiful 1/2 HD.
b) Since the Kobolds only hit my AC on a 20, and I have 18 DEX and weapon specialization in the longbow, I can easily snipe dozens of kobolds while taking no or trivial damage in response.
c) We cast something like dancing lights or lights on the battlement. Then we retreat outside of the range of the kobolds infravision/darkvision, which is probably ruined by the lights anyway, and extinguish our light sources (covering a hooded lantern, for example). At this point, we are completely invisible to the kobolds, but they are completely visible to us.
Once the defenders on the wall are completely suppressed, you send some of the party forward to ascend the wall in whatever their preferred manner is - climb skill, extraordinary jumping ability, spider climb, levitation, grappling hook, etc. Once one is up, they provide a method of entry for the rest of the party.
Any description that begins with some variation on "They close with the wall..." seems wrong to me. Rarely is a defensive position anything but a death trap for monsters, and PC's would I think rightfully expect me to salt the ground in front of the wall with pit traps.