openvswitch: Fix flow mask validation.

[ Upstream commit f2a01517f2a1040a0b156f171a7cefd748f2fd03 ]

Following patch fixes typo in the flow validation. This prevented
installation of ARP and IPv6 flows.

Fixes: 19e7a3df ("openvswitch: Fix NDP flow mask validation")
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Reviewed-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>