We already have a time tested weapon good at taking out small highly maneuverable flying things - the shotgun. Currently, infantry are equipped with assault rifles, but replacing the assault rifle with a powerful shotgun might make sense.
An automated sound/visual drone detection/tracking network could tell the infantry where to aim, and the shotgun does the rest. Ammo is cheap compared to the drones.
2/2
@isaackuo @cstross The thing you're trying to counter is the reconnaissance. (Whether it's on "massing for assault" scale or "is that $POLITICAL_FIGURE?" scale.)
For that, you most want to break the comms loop; you next want to destroy the drone beyond its range of resolution.
Kinetic solutions against individual drones need more range than a shotgun because the range of resolution is greater than shotgun range. (Hence 30mm smart rounds as the reflexive solution.)