core: Preserve IF through call16()

core: Preserve IF through call16()

An intcall should always be invoked with interrupts off, but that is
not necessarily the case for a near or far call; in fact it is quite
the exception.  As such, do not filter IF in our register image, and
for our own internal call16() interface, propagate the protected-mode
IF value into real mode, just as we do for the pm_call interface.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>