nfp: bpf: keep track of the offloaded program

After TC offloads were converted to callbacks we have no choice
but keep track of the offloaded filter in the driver.

The check for nn->dp.bpf_offload_xdp was a stop gap solution
to make sure failed TC offload won't disable XDP, it's no longer
necessary.  nfp_net_bpf_offload() will return -EBUSY on
TC vs XDP conflicts.

Fixes: 3f7889c4 ("net: sched: cls_bpf: call block callbacks for offload")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>