The ornamental design for a filterflange, as shown and described.
FIG. 1 is a front perspective view showing my design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front view thereof, which is the same as the rear view thereof;
FIG. 4 is a right side view thereof, which is the same as the left side view thereof; and,
FIG. 5 is a bottom view thereof.
The portion of the filter flange illustrated in broken lines in FIGS. 1, 3, 4 and 5 shows environmental subject matter, which forms no part of the claimed design,