nfp: bpf: pad code with valid nops

We need to append up to 8 nops after last instruction to make
sure the CPU will not fetch garbage instructions with invalid
ECC if the code store was not initialized.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>