nfp: bpf: ignore helper-related checks for BPF calls in nfp verifier

The checks related to eBPF helper calls are performed each time the nfp
driver meets a BPF_JUMP | BPF_CALL instruction. However, these checks
are not relevant for BPF-to-BPF call (same instruction code, different
value in source register), so just skip the checks for such calls.

While at it, rename the function that runs those checks to make it clear
they apply to _helper_ calls only.

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