cmake: fix struct sockaddr_storage check

CHECK_TYPE_SIZE_PREINCLUDE is an internal, undocumented variable which
was removed in cmake 2.8.1. According to the MSDN docs[1], inclusion
of winsock2.h is sufficient. WIN32_LEAN_AND_MEAN does not really seem
to affect the tests, so remove it too[2].

For the non-windows case, remove inet headers as POSIX only requires
sys/socket.h.

 [1]: http://msdn.microsoft.com/en-us/library/windows/desktop/ms740504%28v=vs.85%29.aspx
 [2]: http://stackoverflow.com/questions/11040133/what-does-defining-win32-lean-and-mean-exclude-exactly



Signed-off-by: Peter Wu <peter@lekensteyn.nl>