misc: Fix various warnings from clippy 0.1.82

An example warning output is:

error: first doc comment paragraph is too long
   --> virtio-devices/src/lib.rs:158:1
    |
158 | / /// Convert an absolute address into an address space (GuestMemory)
159 | | /// to a host pointer and verify that the provided size define a valid
160 | | /// range within a single memory region.
161 | | /// Return None if it is out of bounds or if addr+size overlaps a single region.
    | |_
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#too_long_first_doc_paragraph
    = note: `-D clippy::too-long-first-doc-paragraph` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::too_long_first_doc_paragraph)]`

Signed-off-by: Bo Chen <chen.bo@intel.com>

vm-migration/src/lib.rs

@@ -63,6 +63,7 @@ pub trait Pausable {
 }
 
 /// A Snapshottable component snapshot section.
+///
 /// Migratable component can split their migration snapshot into
 /// separate sections.
 /// Splitting a component migration data into different sections
@@ -94,6 +95,8 @@ impl SnapshotData {
     }
 }
 
+/// Data structure to describe snapshot data
+///
 /// A Snapshottable component's snapshot is a tree of snapshots, where leafs
 /// contain the snapshot data. Nodes of this tree track all their children
 /// through the snapshots field, which is basically their sub-components.
@@ -207,8 +210,9 @@ pub trait Transportable: Pausable + Snapshottable {
     }
 }
 
-/// Trait to be implemented by any component (device, CPU, RAM, etc) that
-/// can be migrated.
+/// Trait to define shared behaviors of components that can be migrated
+///
+/// Examples are device, CPU, RAM, etc.
 /// All migratable components are paused before being snapshotted, and then
 /// eventually resumed. Thus any Migratable component must be both Pausable
 /// and Snapshottable.