net: openvswitch: rename flow_stats to sw_flow_stats

There is a flow_stats structure defined in include/net/flow_offload.h
and a follow up patch adds #include <net/flow_offload.h> to
net/sch_generic.h.

This breaks compilation since OVS codebase includes net/sock.h which
pulls in linux/filter.h which includes net/sch_generic.h.

In file included from ./include/net/sch_generic.h:18:0,
                 from ./include/linux/filter.h:25,
                 from ./include/net/sock.h:59,
                 from ./include/linux/tcp.h:19,
                 from net/openvswitch/datapath.c:24

This definition takes precedence on OVS since it is placed in the
networking core, so rename flow_stats in OVS to sw_flow_stats since
this structure is contained in sw_flow.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>