FIG. 1 is a top, front, left side perspective view of a wall panel embodying our design; FIG. 2 is a front elevational view thereof, the rear elevational view being plain and unornamental; FIG. 3 is a left side elevational view thereof, the right side elevational view being a mirror image thereof; and, FIG. 4 is a top plan view thereof, the bottom plan view being a mirror image thereof.