Update the soilsnow_mask to ensure the correct mask is applied when writing increments

[Yanjun-Gan]

The mask in the file "gridio_gfs.f90" is incorrect. We need to update the code to correctly generate the mask for the output variable "soilsnow_mask":

• 0: Ocean/glacier
• 1: Snow-free land
• 2: Snow-covered land

The code incorrectly classifies snow-covered sea-ice grids as snow-covered land because the variable "weasd" included snow-covered sea-ice grids. Also, glaciers are not being included in 0.