general protection fault in rt6_fill_node

[syzbot]

syzbot suspects this issue was fixed by commit:

commit eeaac3634ee0e3f35548be35275efeca888e9b23
Author: Nikolay Aleksandrov <nikolay at cumulusnetworks.com>
Date:   Sat Aug 22 12:06:36 2020 +0000

    net: nexthop: don't allow empty NHA_GROUP

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=12beed5b900000
start commit:   c3d8f220 Merge tag 'kbuild-fixes-v5.9' of git://git.kernel..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=a0437fdd630bee11
dashboard link: https://syzkaller.appspot.com/bug?extid=81af6e9b3c4b8bc874f8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13ff8539900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=143f3a96900000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: net: nexthop: don't allow empty NHA_GROUP

For information about bisection process see: https://goo.gl/tpsmEJ#bisection