The ornamental design for a footwear upper, as shown and described.
FIG. 1 is a rear perspective view of a footwear upper showing my 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 broken lines in FIGS. 1-7 represent portions of the footwear that form no part of the claimed design. The broken lines which define the bounds of the claimed design form no part thereof.