nfp: bpf: print map lookup problems into verifier log

Use the verifier log to output error messages if map lookup
can't be offloaded.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>