The ornamental design for a funnel, as shown and described.
FIG. 1 is a top, front perspective view of a funnel showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left-side elevational view thereof;
FIG. 5 is a right-side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines in FIG. 1, FIG. 6, and FIG. 7 of the funnel are for the purpose of illustrating environmental structure, and form no part of the claimed design.