The ornamental design for a userinterface, as shown and described.
FIG. 1 is a front perspective view of an ornamental design for a user interface;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a first side view thereof;
FIG. 5 is a second side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines shown in FIGS. 1-8, that are immediately adjacent to the shaded areas, and define unshaded regions, represent the bounds, while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claim.