Update doc for wall_line_count in support.cpp
Update doc for wall_line_count in support.cpp

CURA-2724

alephobjects/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine,ROBO3D/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine