Make sure we move an interrupt vector to the "lowest" priority level if necessary.  Fixes a nasty bug with establishing interrupts "late".  Also make sure we skip the handler being removed when calculating the new "lowest" and "highest" priority level when disestablishing interrupts.  Remove dmesg spam when freeing vectors.
Make sure we move an interrupt vector to the "lowest" priority level if
necessary.  Fixes a nasty bug with establishing interrupts "late".  Also
make sure we skip the handler being removed when calculating the new "lowest"
and "highest" priority level when disestablishing interrupts.  Remove dmesg
spam when freeing vectors.

tested by many, ok marco@, beck@

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