ofproto-dpif-sflow: Recursively examine actions inside clone.

ofproto-dpif-sflow: Recursively examine actions inside clone.

Until now, dpif_sflow_read_actions() has ignored actions inside clone.
This means that sflow missed tnl_push actions inside clone, which OVS
now uses to avoid tx recirculation.  This commit fixes the problem
by making dpif_sflow_read_actions() recursively process actions inside
clone.

In addition, some sflow data needs to be stored and restored in
ofproto-dpif-xlate when native_tunnel_output() is invoked. Otherwise the
output action of underlay bridge is getting counted too when sFlow is set
on the overlay bridge.

Both bugs are connected to sflows and were introduced by the commit in
the "Fixes:" tag below.

Signed-off-by: Zoltan Balogh <zoltan.balogh@ericsson.com>
CC: Sugesh Chandran <sugesh.chandran@intel.com>
Fixes: 7c12dfc527a5 ("tunneling: Avoid datapath-recirc by combining recirc actions at xlate.")
Signed-off-by: Ben Pfaff <blp@ovn.org>