Remove unused mut from buffer.

examples/load_elf.rs

@@ -89,7 +89,7 @@ fn main() {
         0x64, 0x66, 0x0au8
     ];
 
-    let mut packet2 = &mut [
+    let packet2 = &mut [
         0x01, 0x23, 0x45, 0x67, 0x89, 0xab,
         0xfe, 0xdc, 0xba, 0x98, 0x76, 0x54,
         0x08, 0x00, // ethertype