openvswitch: Use parallel_ops genl.

OVS locking was recently changed to have private OVS lock which
simplified overall locking.  Therefore there is no need to have
another global genl lock to protect OVS data structures.  Following
patch uses of parallel_ops genl family for OVS.  This also allows
more granual OVS locking using ovs_mutex for protecting OVS data
structures, which gives more concurrencey.  E.g multiple genl
operations OVS_PACKET_CMD_EXECUTE can run in parallel, etc.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>