[Buildroot] [PATCH/next 1/1] package/iputils: fix build with nettle

[Petr Vorel]

Hi,

> Fixes:
>  - http://autobuild.buildroot.org/results/e86555090e27b631ba35214ef100aa9331844684

FYI this fixes failures for other archs (I guess incomplete list):
      riscv64 |              iputils-s20190515 | http://autobuild.buildroot.net/results/f78ac0d3c9a679a584bd54ac7f908390f5a4087b
       xtensa |              iputils-s20190515 | http://autobuild.buildroot.net/results/a15323897950f8166f2b14f235a36cd88387d5de

Kind regards,
Petr