On CPUs without support for unrestricted guests DPL cannot be smaller
than RPL for data segments during guest entry, but this state can occurs
if a data segment selector changes while vcpu is in real mode to a value
with lowest two bits != 00. Fix that by forcing DPL == RPL on transition
to protected mode.

This is a regression introduced by c865c43d.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>