clippy: Address the issue 'needless-borrow'

Issue from beta verion of clippy:

Error:    --> vm-virtio/src/queue.rs:700:59
    |
700 |             if let Some(used_event) = self.get_used_event(&mem) {
    |                                                           ^^^^ help: change this to: `mem`
    |
    = note: `-D clippy::needless-borrow` implied by `-D warnings`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

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

net_util/src/mac.rs

@@ -57,7 +57,7 @@ impl MacAddr {
         // TODO: using something like std::mem::uninitialized could avoid the extra initialization,
         // if this ever becomes a performance bottleneck.
         let mut bytes = [0u8; MAC_ADDR_LEN];
-        bytes[..].copy_from_slice(&src);
+        bytes[..].copy_from_slice(src);
 
         MacAddr { bytes }
     }