datapath-windows: Fix CtrlLock acquire issue in OvsReadEventCmdHandler

OvsReadEventCmdHandler was calling OvsRemoveEventEntry after acquiring
CtrlLock. OvsRemoveEventEntry in turn also tries to acquire the same lock.

Added a new lock in Event.c for the eventQueue.

Signed-off-by: Ankur Sharma <ankursharma@vmware.com>
Acked-by: Eitan Eliahu <eliahue@vmware.com>
Acked-by: Sorin Vinturis <svinturis@cloudbasesolutions.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>