KVM: VMX: Fix x2APIC MSR intercept handling on !APICV platforms

Fix an inverted flag for intercepting x2APIC MSRs and intercept writes
by default, even when APICV is enabled.

Fixes: 3eb90017 ("KVM: x86: VMX: Prevent MSR passthrough when MSR access is denied")
Co-developed-by: Peter Xu <peterx@redhat.com>
[sean: added changelog]
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20201005195532.8674-2-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>