vm-migration: add connections field to API

And wire everything up. From now on the multiple connections feature can
be used.

This commit series is heavily based on Julian Stecklina's work, so kudos
to him!

Co-authored-by: Julian Stecklina <julian.stecklina@cyberus-technology.de>
On-behalf-of: SAP sebastian.eydam@sap.com
Signed-off-by: Sebastian Eydam <sebastian.eydam@cyberus-technology.de>

vmm/src/lib.rs

@@ -6,7 +6,6 @@
 use std::collections::HashMap;
 use std::fs::File;
 use std::io::{Read, Write, stdout};
-use std::num::NonZero;
 use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
 use std::panic::AssertUnwindSafe;
 #[cfg(feature = "guest_debug")]
@@ -1367,7 +1366,7 @@ impl Vmm {
         } else {
             let mut mem_send = migration_transport::SendAdditionalConnections::new(
                 &send_data_migration.destination_url,
-                NonZero::new(1).unwrap(),
+                send_data_migration.connections,
                 &vm.guest_memory(),
             )?;