net_util, virtio-devices, vhost_user_net: Relocate {Rx,Tx}Virtio

By moving the code for opening the two RX and TX queues into a shared
location we are starting to remove the requirement for the
vhost-user-net backend to depend on the virtio-devices crate which in of
itself depends on many other crates that are not necessary for the
backend to function.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

net_util/Cargo.toml

@@ -5,10 +5,13 @@ authors = ["The Chromium OS Authors"]
 
 [dependencies]
 libc = "0.2.72"
+log = "0.4.8"
 net_gen = { path = "../net_gen" }
 rand = "0.7.3"
 serde = "1.0.114"
 virtio-bindings = "0.1.0"
+vm-memory = { version = "0.2.1", features = ["backend-mmap", "backend-atomic"] }
+vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = ">=0.3.1"
 
 [dev-dependencies]