tests: Extend test_tap_from_fd to reboot

Check that the VM comes back with the correct network setup after a
reboot.

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

tests/integration.rs

@@ -5393,6 +5393,17 @@ mod tests {
                         .unwrap_or_default(),
                     2
                 );
+                guest.ssh_command("sudo reboot").unwrap();
+                guest.wait_vm_boot(None).unwrap();
+                assert_eq!(
+                    guest
+                        .ssh_command("ip -o link | wc -l")
+                        .unwrap()
+                        .trim()
+                        .parse::<u32>()
+                        .unwrap_or_default(),
+                    2
+                );
             });
 
             let _ = child.kill();