vhost-user_net, vm-virtio, vmm: Permit host MAC address setting

Add a new "host_mac" parameter to "--net" and "--net-backend" and use
this to set the MAC address on the tap interface. If no address is given
one is randomly assigned and is stored in the config.

Support for vhost-user-net self spawning was also included.

Fixes: #1177

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

vm-virtio/src/net_util.rs

@@ -119,6 +119,8 @@ pub enum Error {
     TapSetIp(TapError),
     /// Setting tap netmask failed.
     TapSetNetmask(TapError),
+    /// Setting MAC address failed
+    TapSetMac(TapError),
     /// Setting tap interface offload flags failed.
     TapSetOffload(TapError),
     /// Setting vnet header size failed.
@@ -531,6 +533,7 @@ pub fn open_tap(
     if_name: Option<&str>,
     ip_addr: Option<Ipv4Addr>,
     netmask: Option<Ipv4Addr>,
+    host_mac: Option<MacAddr>,
     num_rx_q: usize,
 ) -> Result<Vec<Tap>> {
     let mut taps: Vec<Tap> = Vec::new();
@@ -558,6 +561,9 @@ pub fn open_tap(
             if let Some(mask) = netmask {
                 tap.set_netmask(mask).map_err(Error::TapSetNetmask)?;
             }
+            if let Some(mac) = host_mac {
+                tap.set_mac_addr(mac).map_err(Error::TapSetMac)?
+            }
             tap.enable().map_err(Error::TapEnable)?;
             tap.set_offload(flag).map_err(Error::TapSetOffload)?;