netdev: Dynamic per-port Flow API.

Current issues with Flow API:

* OVS calls offloading functions regardless of successful
  flow API initialization. (ex. on init_flow_api failure)
* Static initilaization of Flow API for a netdev_class forbids
  having different offloading types for different instances
  of netdev with the same netdev_class. (ex. different vports in
  'system' and 'netdev' datapaths at the same time)

Solution:

* Move Flow API from the netdev_class to netdev instance.
* Make Flow API dynamic, i.e. probe the APIs and choose the
  suitable one.

Side effects:

* Flow API providers localized as possible in their modules.
* Now we have an ability to make runtime checks. For example,
  we could check if particular device supports features we
  need, like if dpdk device supports RSS+MARK action.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Acked-by: Roi Dayan <roid@mellanox.com>

lib/netdev-linux.c

@@ -55,7 +55,6 @@
 #include "hash.h"
 #include "openvswitch/hmap.h"
 #include "netdev-provider.h"
-#include "netdev-tc-offloads.h"
 #include "netdev-vport.h"
 #include "netlink-notifier.h"
 #include "netlink-socket.h"
@@ -3321,7 +3320,6 @@ exit:
 
 const struct netdev_class netdev_linux_class = {
     NETDEV_LINUX_CLASS_COMMON,
-    LINUX_FLOW_OFFLOAD_API,
     .type = "system",
     .construct = netdev_linux_construct,
     .get_stats = netdev_linux_get_stats,
@@ -3341,7 +3339,6 @@ const struct netdev_class netdev_tap_class = {
 
 const struct netdev_class netdev_internal_class = {
     NETDEV_LINUX_CLASS_COMMON,
-    LINUX_FLOW_OFFLOAD_API,
     .type = "internal",
     .construct = netdev_linux_construct,
     .get_stats = netdev_internal_get_stats,