ng_sample: improve styling

[p.mousavizadeh_protonmail.com]

Summary

Most of the developers used the (resp == NULL) style in their code. New developers will try to follow the ng_sample and may use the (!resp) style which is not consistent with other netgraph modules, also not recommended by MISRA-C.

[ivy]

sys/netgraph/ng_sample.c

323

while you're here, i believe this extra space is a typo that could be removed.

[kp]

We don't follow MISRA-C, but style(9) does also require this, so the change should be made anyway.

[p.mousavizadeh_protonmail.com]

• ng_sample: apply style(9)

[p.mousavizadeh_protonmail.com]

Done

[des]

@ivy why don't you land this