datapath-windows: Removed gOvsCtrlLock global spinlock

datapath-windows: Removed gOvsCtrlLock global spinlock

There is no need to use gOvsCtrlLock spinlock to guard the switch
context, as there is now the switch context's reference count used
for this purpose.

Now the gOvsCtrlLock spinlock guards only one shared resource, the
OVS_OPEN_INSTANCE global instance array.

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