misc: Adapt consistent import style formatting

Historically the Cloud Hypervisor coding style has been to ensure that
all imports are ordered and placed in a single group. Unfortunately
cargo fmt has no support for ensuring that all imports are in a single
group so if whitespace lines were added as part of the import statements
then they would only be odered correctly in the group.

By adopting "group_imports="StdExternalCrate" we can enforce a style
where imports are placed in at most three groups for std, external
crates and the crate itself. Choosing a style enforceable by the tooling
reduces the reviewer burden.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>

virtio-devices/src/net.rs

@@ -5,6 +5,36 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the THIRD-PARTY file.
 
+use std::collections::HashMap;
+use std::net::Ipv4Addr;
+use std::num::Wrapping;
+use std::ops::Deref;
+use std::os::unix::io::{AsRawFd, RawFd};
+use std::result;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Barrier};
+use std::thread;
+
+use anyhow::anyhow;
+#[cfg(not(fuzzing))]
+use net_util::virtio_features_to_tap_offload;
+use net_util::CtrlQueue;
+use net_util::{
+    build_net_config_space, build_net_config_space_with_mq, open_tap, MacAddr, NetCounters,
+    NetQueuePair, OpenTapError, RxVirtio, Tap, TapError, TxVirtio, VirtioNetConfig,
+};
+use seccompiler::SeccompAction;
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+use virtio_bindings::virtio_config::*;
+use virtio_bindings::virtio_net::*;
+use virtio_bindings::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
+use virtio_queue::{Queue, QueueT};
+use vm_memory::{ByteValued, GuestAddressSpace, GuestMemoryAtomic};
+use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
+use vm_virtio::AccessPlatform;
+use vmm_sys_util::eventfd::EventFd;
+
 use super::Error as DeviceError;
 use super::{
     ActivateError, ActivateResult, EpollHelper, EpollHelperError, EpollHelperHandler,
@@ -15,34 +45,6 @@ use crate::seccomp_filters::Thread;
 use crate::thread_helper::spawn_virtio_thread;
 use crate::GuestMemoryMmap;
 use crate::VirtioInterrupt;
-use anyhow::anyhow;
-#[cfg(not(fuzzing))]
-use net_util::virtio_features_to_tap_offload;
-use net_util::CtrlQueue;
-use net_util::{
-    build_net_config_space, build_net_config_space_with_mq, open_tap, MacAddr, NetCounters,
-    NetQueuePair, OpenTapError, RxVirtio, Tap, TapError, TxVirtio, VirtioNetConfig,
-};
-use seccompiler::SeccompAction;
-use serde::{Deserialize, Serialize};
-use std::collections::HashMap;
-use std::net::Ipv4Addr;
-use std::num::Wrapping;
-use std::ops::Deref;
-use std::os::unix::io::{AsRawFd, RawFd};
-use std::result;
-use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, Barrier};
-use std::thread;
-use thiserror::Error;
-use virtio_bindings::virtio_config::*;
-use virtio_bindings::virtio_net::*;
-use virtio_bindings::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
-use virtio_queue::{Queue, QueueT};
-use vm_memory::{ByteValued, GuestAddressSpace, GuestMemoryAtomic};
-use vm_migration::{Migratable, MigratableError, Pausable, Snapshot, Snapshottable, Transportable};
-use vm_virtio::AccessPlatform;
-use vmm_sys_util::eventfd::EventFd;
 
 /// Control queue
 // Event available on the control queue.