message: Fix build on architectures with unsigned char
  ARM and POWER are affected.
diff: @@ -129,7 +129,7 @@ pub fn channel(network_interface: &NetworkInterface, config: Config) -> io::Resu
  }
  let mut iface: bpf::ifreq = unsafe { mem::zeroed() };
  for (i, c) in network_interface.name.bytes().enumerate() {
  - iface.ifr_name[i] = c as i8;
  + iface.ifr_name[i] = c as libc::c_char;
  }
  let buflen = config.read_buffer_size as libc::c_uint;
  