The ornamental design for arm extension and headrest for massage table, as shown and described.
FIG. 1 is a slightly reduced top perspective view of an arm extension and headrest for massage table showing my new design;
FIG. 2 is another top perspective view thereof;
FIG. 3 is a bottom perspective view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a left side view thereof;
FIG. 8 is a top view thereof; and,
FIG. 9 is a bottom view thereof.
The broken line showing a massage table and connector rods is included for the purpose of illustrating environment and forms no part of the claimed design.