freebsd: Fix type of struct xktls_session_onedir, field ifnet

For the upstream definition, see:

freebsd/freebsd-src@c9e9a0f

Author: neuschaefer

src/unix/bsd/freebsdlike/freebsd/mod.rs

@@ -1724,7 +1724,7 @@ s_no_extra_traits! {
         pub tls_bs: u8,
         pub flags: u8,
         pub drv_st_len: u16,
-        pub ifnet: [u8; 16],
+        pub ifnet: [c_char; 16],
     }
 
     pub struct xktls_session {