misc: Change cpu ID type from u8 to u32

This is the first change to Cloud Hypervisor in a series of changes
intended to increase the max number of supported vCPUs in guest VMs,
which is currently limited to 255 (254 on x86_64).

No user-visible/behavior changes are expected as a result of
applying this patch, as the type of boot_cpus and related
fields in config structs remains u8 for now, and all configuration
validations remain the same.

Signed-off-by: Barret Rhoden <brho@google.com>
Signed-off-by: Neel Natu <neelnatu@google.com>
Signed-off-by: Ofir Weisse <oweisse@google.com>
Signed-off-by: Peter Oskolkov <posk@google.com>

vmm/src/api/mod.rs

@@ -217,7 +217,7 @@ pub struct VmmPingResponse {
 
 #[derive(Clone, Deserialize, Serialize, Default, Debug)]
 pub struct VmResizeData {
-    pub desired_vcpus: Option<u8>,
+    pub desired_vcpus: Option<u32>,
     pub desired_ram: Option<u64>,
     pub desired_balloon: Option<u64>,
 }
@@ -307,7 +307,7 @@ pub trait RequestHandler {
 
     fn vm_resize(
         &mut self,
-        desired_vcpus: Option<u8>,
+        desired_vcpus: Option<u32>,
         desired_ram: Option<u64>,
         desired_balloon: Option<u64>,
     ) -> Result<(), VmError>;