openvswitch: Move key_attr_size() to flow_netlink.h.

flow-netlink has netlink related code.

Signed-off-by: Joe Stringer <joestringer@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>

diff --cc net/openvswitch/datapath.c
Simple merge

diff --cc net/openvswitch/flow_netlink.c
Simple merge

diff --cc net/openvswitch/flow_netlink.h
Simple merge