nfp: bpf: relax prog rejection through max_pkt_offset

NFP is refusing to offload programs whenever the MTU is set to a value
larger than the max packet bytes that fits in NFP Cluster Target Memory
(CTM). However, a eBPF program doesn't always need to access the whole
packet data.

Verifier has always calculated maximum direct packet access (DPA) offset,
and kept it in max_pkt_offset inside prog auxiliar information. This patch
relax prog rejection based on max_pkt_offset.

Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>