net: flow_table: drop 'hw_' prefix and replace with 'net_'

The namespace flow_* created conflicts with other namespaces mostly
in OVS subsystem so I went with net_flow_*. This seems specific
enough to explain the flow table model we are using and also wont
create a strange naming convention if we use this with software
device later on.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
net: flow_table remove unused calls
net: flow_table: field ref is a single object use one netlink attrib

Some of these objects can be sent as single objects.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
net: flow_table: remove FLOW_FLOW strings and cleanup graph types

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>