The ornamental design for a headset, as shown and described.
FIG. 1 is a perspective front view of a headset showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a rear view thereof.
The broken line showing of the environmental structure of the headset in FIGS. 1–7 is for environmental purposes only and forms no part of the claimed design.