Re-instate code network settings code in the co-installer

Re-instate code network settings code in the co-installer

This functionality was moved into XENVIF when it transpired that it did not
work with Windows 10. However, attempting to mess with network settings in
a driver has also proved to have problematic corner cases.

This patch re-instates old code but changes the mechnism for acquiring
network settings from an emulated device. Instead of attempting to copy
settings to a new stack binding (which failed on Windows 10 because the
stack binding was not set up), the stack binding of the emulated device is
cloned. This is done in post-install phase if the emulated device is online
(otherwise Windows will refuse to start the PV device) or in pre-install
phase if the emulated device is offline, as is the case when re-installing
XENNET. This appears to work reliably across all variants of Windows.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>