The ornamental design for footwear upper, as shown and described.
FIG. 1 is a perspective view of the footwear upper embodying the new design;
FIG. 2 is a top 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 rear view thereof.
The dashed lines represent unclaimed stitching. The dash dot dot dash lines are shown for environmental purposes and do not form any part of the claimed design. Further, the dash dot dot dash lines immediately adjacent the solid-line portions of the design form the boundary of the design, and forms no part of the claimed design.