SOCKET_CONTEXT / IOCTL_AFD_SET_CONTEXT helper data format is unknown

_From [timurrrr@google.com](https://code.google.com/u/timurrrr@google.com/) on May 30, 2011 04:33:39_

On W7 x64 the SizeOfHelperData is 4 and all the bytes after the remote address are initialized (on the issue #421 test).

On XP 32 (and maybe 64-bit too) the SizeOfHelperData is more (104 on 32-bit) and some data in the middle is uninit.

The current comment in drmemory/syscall_windows.c says:
/\* XXX: helper data could be a struct w/ padding. I have seen pieces of
\* it be uninit on XP. If see many false positives here should just
\* disable this until understand its structure.
*/

xref issue #375

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=424_