switch to MCLGETI.
switch to MCLGETI.

this conversion is the easiest ive done so far. the mbuf allocation wrapper
in the driver already had code to handle a failing cluster allocator as
part of a test harness, now we test that code all the time with MCLGETI.

ok kettenis@
tested by phessler@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars