The ornamental design for a socketstrip, as shown and described.
FIG. 1 is a front and left side perspective view of a socket strip, showing our new design in an open position with the socket strip fully extended through the base plate;
FIG. 2 is a front view thereof;
FIG. 3 is a right side view thereof, with the left side view being a mirror image thereof;
FIG. 4 is a rear view thereof; and,
FIG. 5 is a first end view thereof, in a closed position with the socket strip fully inserted through the base plate.
The areas and features shown in broken lines represent environmental structure only and form no part of the claimed design.