Next argument after the tc opcode/verdict is optional, using NEXT_ARG()
requires to have another argument after that one otherwise tc will bail
out. Therefore, we need to advance to the next argument manually as done
elsewhere.

Fixes: 86ab59a6 ("tc: add support for BPF based actions")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Pirko <jiri@resnulli.us>