Add defines, enums and headers for MSVC

Add defines needed to compile netlink-socket.c and netlink.c.

Add a wrapper and the functionality behind it for syconf.

Add the newly created files to the noinst_HEADERS in windows/automake.mk

Signed-off-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>