Enable WITH_UPSTREAM_LIBCOAP on Windows

Enable WITH_UPSTREAM_LIBCOAP on Windows

Make Windows start using the upstream libcoap rather than the forked
version

Change-Id: Iae4257d4f8246e033116381ef058668180e11ee2
Signed-off-by: Dave Thaler <dthaler@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/10041
Reviewed-by: David Antler <david.a.antler@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>