Windows: np AddConnection error code

If AddConnection fails because DeviceIOcontrol fails, do not
return out of memory which is an unsupported error code.  Report
a network failure.

Change-Id: Ib0c83a2fc0b681a94483e1b16ab102354767c993
Reviewed-on: http://gerrit.openafs.org/10149
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>