We claim the ornamental design for an ironing board, as shown and described.
FIG. 1 is a perspective view of an ironing board showing the new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a perspective view of the ironing board shown in an alternate configuration with the sleeve board and a hanger fixed to the control tower unfolded; and,
FIG. 9 is a front perspective view of the ironing board folded.
The broken lines shown in the drawing figures depict portions of the ironing board that form no part of the claimed design.