setting a dump device as a side effect of getattr

[Matthew Jacob]

The current mechanism for setting a dump device is to run down the list 
of geoms and call set_dumper at the bottom layer.

Would anyone object to making the caller of the GETTATTR for 
GEOM::kerneldump responsible for calling set_dumper (if desired)?

This gives systems some flexibility in changing or extending dump 
devices w/o having to play games witth doing save of the current dumper, 
calling the GETATTR, restoring the current dumper and so on.