Document MAC address selection and setting for atse(4).

Submitted by:	brooks
MFC after:	3 days
Sponsored by:	DARPA/AFRL
vt(4): Handle global and per-window mouse cursor toggle in one place

Before the global flag was set/unset using the CONS_MOUSECTL ioctl, and
the per-window flag through the MOUSE_SETLEVEL or MOUSE_SETMODE ioctls.

Also, if the cursor is already enabled/disabled, return immediatly. This
avoids to reset the cursor's position to the center of the screen.

This matches syscons' behavior.

While here, remove a trailing space and a redundant variable
declaration.