KVM: X86: Filter out the broadcast dest for IPI fastpath

Except destination shorthand, a destination value 0xffffffff is used to
broadcast interrupts, let's also filter out this for single target IPI
fastpath.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1585815626-28370-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>