nfp: bpf: use extack support to improve debugging

Use the recently added extack support for eBPF offload in the driver.

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