Windows: NPCancelConnection without drive letter

When canceling a network connection to a UNC path, do not match
connections that have drive letters assigned.  Only cancel the connection
if there it matches the UNC path and has no local name.

Change-Id: I2c27c6d08cec65406f7e7f9eb61cd6d6c7be1f5c
Reviewed-on: http://gerrit.openafs.org/9640
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Peter Scott <pscott@kerneldrivers.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>