The ornamental design for a mountingfixture, as shown and described.
FIG. 1 is a lower perspective view of a sixth embodiment of the invention
FIG. 2 is an upper perspective view of a sixth embodiment
FIG. 3 is a top plan view of a sixth embodiment
FIG. 4 is a bottom plan view of a sixth embodiment
FIG. 5 is a front plan view of a sixth embodiment
FIG. 6 is a back view of a sixth embodiment; and,
FIG. 7 is a left side plan view of a sixth embodiment, but side views being symmetric/mirror images.
Broken lines in the drawings are included for the purpose of illustrating an environment and form no part of the claimed design. The claimed invention can be used in other environments.