qga: win32 qmp_guest_network_get_interfaces implementation

qga: win32 qmp_guest_network_get_interfaces implementation

By default, IPv4 prefixes will be derived by matching the address
to those returned by GetAdaptersInfo.  IPv6 prefixes can not be
matched this way due to the unpredictable order of entries.

In Windows Vista/2008 guests and newer, both IPv4 and IPv6 prefixes
can be retrieved from OnLinkPrefixLength.  Setting --extra-cflags
in the build configuration to "-D_WIN32_WINNT=0x600"
or greater makes OnLinkPrefixLength available.  Setting --extra-cflags
is not required and if not set, the default approach to get the prefix
will be taken.

Signed-off-by: Kirk Allan <kallan@suse.com>
* drop ws2ipdef.h, it's missing on old mingw, and ws2tcpip.h already
  includes it automatically on new builds
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>