The ornamental design for the recess plug, as shown and described.
FIG. 1 is a front perspective view of a recess plug showing the new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a top plan view thereof with a bottom plan view being a mirror image thereof;
FIG. 4 is a right side elevation view thereof with the left side elevation view being a mirror image thereof; and,
FIG. 5 is a back elevation view thereof.
The surface shading lines on the claimed portion are provided only to indicate the character and/or any contour or curvature of the surfaces. They do not indicate color, texture, markings that actually exist thereon, indicia, graphic representations, surface treatment, or any other ornamentation applied to the article.