nfp: bpf: release the reference on offloaded programs

The xdp_prog member of the adapter's data path structure is used
for XDP in driver mode.  In case a XDP program is loaded with in
HW-only mode, we need to store it somewhere else.  Add a new XDP
prog pointer in the main structure and use that when we need to
know whether any XDP program is loaded, not only a driver mode
one.  Only release our reference on adapter free instead of
immediately after netdev unregister to allow offload to be disabled
first.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>