vmm: allow comparing commands and extracting response length

This will be useful later when we rebuild the live migration code as a
state machine.

On-behalf-of: SAP julian.stecklina@sap.com
Signed-off-by: Julian Stecklina <julian.stecklina@cyberus-technology.de>

vm-migration/src/protocol.rs

@@ -52,7 +52,7 @@ use crate::bitpos_iterator::BitposIteratorExt;
 // The source can at any time send an "abandon request" to cancel
 
 #[repr(u16)]
-#[derive(Copy, Clone, Default)]
+#[derive(Debug, Copy, Clone, Default, PartialEq, Eq)]
 pub enum Command {
     #[default]
     Invalid,
@@ -176,6 +176,10 @@ impl Response {
         self.status
     }
 
+    pub fn length(&self) -> u64 {
+        self.length
+    }
+
     pub fn read_from(fd: &mut dyn Read) -> Result<Response, MigratableError> {
         let mut response = Response::default();
         fd.read_exact(Self::as_mut_slice(&mut response))