The ornamental design for a gateway, as shown and described.
FIG. 1 is a rear bottom perspective view of a gateway showing our new design;
FIG. 2 is a bottom view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a left side view thereof.
The unshaded areas, including those unshaded areas within the triangular shapes on the bottom of the device, form no part of the claimed design. The uneven-length broken lines immediately adjacent to the shaded area represent the bounds of the claimed design and forms no part thereof. The even-length broken lines depicting the remainder of the gateway form no part of the claimed design.