net_util: Address Rust 1.51.0 clippy issue (redundant_slicing)

error: redundant slicing of the whole range
  --> net_util/src/mac.rs:60:35
   |
60 |         bytes[..].copy_from_slice(&src[..]);
   |                                   ^^^^^^^^ help: use the original slice instead: `src`
   |
   = note: `-D clippy::redundant-slicing` implied by `-D warnings`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_slicing

Signed-off-by: Rob Bradford <robert.bradford@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 }
     }