KVM: nVMX: Move nested VM-Exit tracepoint into nested_vmx_reflect_vmexit()

Move the tracepoint for nested VM-Exits in preparation of splitting the
reflection logic into L1 wants the exit vs. L0 always handles the exit.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200415175519.14230-5-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>