KVM: selftests: Verify VMX MSRs can be restored to KVM-supported values

Verify that KVM allows toggling VMX MSR bits to be "more" restrictive,
and also allows restoring each MSR to KVM's original, less restrictive
value.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220607213604.3346000-16-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>