The ornamental design for a funnel, as shown and described.
FIG. 1 is a left side elevation view of a funnel showing my new design, wherein a right side elevation view (not shown) thereof is a mirror image of the left side elevation view.
FIG. 2 is a left side sectional view along an axial section plane thereof, wherein a right side sectional view (not shown) thereof along the axial section plane is a mirror image of the left side sectional view.
FIG. 3 is a top left front perspective view thereof, wherein a top right front perspective view (not shown) thereof is a mirror image of the top left front perspective view; and,
FIG. 4 is a bottom right rear perspective view thereof, wherein a bottom left rear perspective view (not shown) thereof is a mirror image of the bottom right rear perspective view.