I claim the ornamental design for a driveshaft tunnel, as shown and described.
FIG. 1 is a perspective side view of a driveshaft tunnel shaped according to the design;
FIG. 2 is a top view of the design;
FIG. 3 is a side view of the design, the opposite side being the mirror image thereof;
FIG. 4 is an end view of the design;
FIG. 5 is an opposite end view of the design; and,
FIG. 6 is a bottom view of the design.
The broken line showing of portions of the driveshaft tunnel is included for the purpose of illustrating environmental structure and forms no part of the claimed design.