On long-mode, when far call that changes cs.l takes place, the stack size is
determined by the new mode. For instance, if we go from 32-bit mode to 64-bit
mode, the stack-size if 64. KVM uses the old stack size.
Fix it.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>