The ornamental design for a footwear upper, as shown and described.
FIG. 1 is a front perspective view of a footwear upper showing the new design;
FIG. 2 is a side elevational view thereof;
FIG. 3 is an opposite side elevational view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The evenly spaced broken lines represent portions of the footwear that form no part of the claimed design. Further, the dash dot dash lines immediately adjacent to the solid-line portions of the design form the bounds of the design, and forms no part of the claimed design.