We claim the ornamental design for a mounting support, as shown and described.
FIG. 1 is a perspective view of the claimed design according to an embodiment;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a front elevation view thereof; and,
FIG. 7 is a rear elevation view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines formed by dashes show unclaimed subject matter and form no part of the claimed design. The internal surface of the mounting support is devoid of any ornamentation.