fix: Downgrade wrongly placed doc coment to normal comment

Kani, running using nightly rustc, was warning about this comment. Fix
it to resolve the warning during verification, to get slightly cleaner
logs.

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

src/vmm/src/vmm_config/net.rs

@@ -84,7 +84,7 @@ impl NetBuilder {
     /// Creates an empty list of Network Devices.
     pub fn new() -> Self {
         NetBuilder {
-            /// List of built network devices.
+            // List of built network devices.
             net_devices: Vec::new(),
         }
     }