Add smoke shells to the "AT" Field guns

[GuardianReaper0]

Some of the tanks now have smoke shells, though I rarely see them used. It would be nice if the field guns that engineer squads can build could also have some smoke shells to fire.

[tommyZZM]

I understand the truth, but we only have anti-tank guns, no official field guns, and anti-tank guns usually don’t play the role of shooting smoke shells