xtables: silence two compiler warnings

xtables: silence two compiler warnings

inlined from ‘do_commandarp’ at xtables-arp.c:1198:16:
xtables-arp.c:844:2: warning: ‘strncpy’ specified bound 29 equals destination size [-Wstringop-truncation]
  strncpy(target->t->u.user.name, jumpto, sizeof(target->t->u.user.name));
xtables-eb-translate.c: In function ‘do_commandeb_xlate’:
xtables-eb-translate.c:285:6: warning: unused variable ‘chcounter’ [-Wunused-variable]
  int chcounter = 0; /* Needed for -C */
      ^~~~~~~~~
Signed-off-by: Florian Westphal <fw@strlen.de>