Qemu will send GET_INFLIGHT_FD and SET_INFLIGH_FD to backend, and
the backend setup the inflight memory to track the io.

Change-Id: I805d6189996f7a1b44c65f0b12ef7473b1789510
Signed-off-by: Li Feng <fengli@smartx.com>
Message-Id: <20200909122021.1055174-1-fengli@smartx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>