The ornamental design for a surfaceconfiguration of a diffuser for a bumper of a vehicle, as shown and described.
FIG. 1 is a left perspective view of a surface configuration of a diffuser for a bumper of a vehicle according to my novel design;
FIG. 2 is a right perspective view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a front view thereof; and,
FIG. 6 is a left perspective view thereof, showing the placement on the bumper.
The broken lines are for illustrative purposes only and form no part of the claimed design. Also enclosed is a set of photographs of an embodiment of the design.