message: Fix c_void pointer cannot be offset
diff: @@ -24,6 +24,7 @@ use std::mem;
  use std::slice;
  use std::str::from_utf8_unchecked;
  use std::sync::Arc;
  +use self::winapi::ctypes::c_char;
  struct WinPcapAdapter {
  adapter: winpcap::LPADAPTER,
  @@ -242,8 +243,8 @@ impl DataLinkReceiver for DataLinkReceiverImpl {
  0 => return Err(io::Error::last_os_error()),
  _ => unsafe { (*self.packet.packet).ulBytesReceived as isize },
  };
  - let mut ptr = unsafe { (*self.packet.packet).Buffer };
  - let end = unsafe { (*self.packet.packet).Buffer.offset(buflen) };
  + let mut ptr = unsafe { (*self.packet.packet).Buffer as *mut c_char};
  + let end = unsafe { ((*self.packet.packet).Buffer as *mut c_char).offset(buflen) };
  while ptr < end {
  unsafe {
  let packet: *const bpf::bpf_hdr = mem::transmute(ptr);
  