openvswitch: Fix incorrect type use.

Patch fixes following sparse warning.
net/openvswitch/flow_netlink.c:583:30: warning: incorrect type in assignment (different base types)
net/openvswitch/flow_netlink.c:583:30:    expected restricted __be16 [usertype] ipv4
net/openvswitch/flow_netlink.c:583:30:    got int

Fixes: 6b26ba3a ("openvswitch: netlink attributes for IPv6 tunneling")
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>