The ornamental design for a bootshaft, as shown and described.
FIG. 1 is a perspective view of a boot shaft according to the present invention.
FIG. 2 is a right side elevational view of the boot shaft.
FIG. 3 is a left side elevational view of the boot shaft.
FIG. 4 is a rear elevational view of the boot shaft; and,
FIG. 5 is a front elevational view of the boot shaft.
The broken lines are solely for the purpose of illustrating unclaimed areas and form no part of the claimed design. The claimed design is intended to encompass a boot shaft as shown and a second embodiment that is the opposite matching boot shaft, i.e., the mirror image of that shown.