misc: Use c"" to construct nul-terminated string

As clippy of rust-toolchain version 1.83.0-beta.1 suggests, use `c""` to
construct nul-terminated `CStr`.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

net_util/src/tap.rs

@@ -124,7 +124,7 @@ impl Tap {
             // Open calls are safe because we give a constant null-terminated
             // string and verify the result.
             libc::open(
-                b"/dev/net/tun\0".as_ptr() as *const c_char,
+                c"/dev/net/tun".as_ptr() as *const c_char,
                 flags.unwrap_or(libc::O_RDWR | libc::O_NONBLOCK | libc::O_CLOEXEC),
             )
         };