Re-add impls for Eq,Ord and Hash for MmapXenFlags

With the upgrade to the 2.0 series of bitflags, these were no longer
automatically derived.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

src/mmap_xen.rs

@@ -432,7 +432,7 @@ impl Drop for MmapUnix {
 // Bit mask for the vhost-user xen mmap message.
 bitflags! {
     /// Flags for the Xen mmap message.
-    #[derive(Copy, Clone, Debug)]
+    #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
     pub struct MmapXenFlags: u32 {
         /// Standard Unix memory mapping.
         const UNIX = 0x0;