The ornamental design for a footwear upper, as shown and described.
FIG. 1 is a top, right perspective view of a footwear upper showing my new design.
FIG. 2 is a right side elevational view thereof.
FIG. 3 is a left side elevational view thereof.
FIG. 4 is a front elevational view thereof.
FIG. 5 is a rear elevational view thereof.
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a top plan view thereof.
The broken lines showing the other footwear features are for the purpose of illustrating environmental structure and form no part of the claimed design.