cam: Add probes for xpt actions

[imp]

Summary

cam::xpt:action(union ccb *)
cam::xpt:done((union ccb *)
cam::xpt:async-cb(void *cbarg, uint32_t async_code, struct cam_path
*path, void *async_arg);

Called when xpt_action(), xpt_done*() and the xpt async callbacks are
called.

Sponsored by: Netflix

[ziaee]

I really like the way you used Fn here so it doesn't cause collisions in the whatis database!

share/man/man4/dtrace_cam.4

11

Maybe?

[ziaee]

share/man/man4/dtrace_cam.4

33