datapath-windows: rename 'hvDeleted' to 'isPresentOnHv'

datapath-windows: rename 'hvDeleted' to 'isPresentOnHv'

'hvDeleted' was originally added to track vports that got deleted from
the Hyper-V switch, but which still exists in OVS. Since then, it has
taken a new meaning: eg. it is set to TRUE for VXLAN ports which don't
exist on the Hyper-V switch at all.

Hence renaming it to something more appropriate.

Signed-off-by: Nithin Raju <nithin@vmware.com>
Acked-by: Sorin Vinturis <svinturis@cloudbasesolutions.com>
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>