net: fib_notifier: don't return positive values on fib registration

mainline inclusion
from mainline-v5.12-rc1
commit 6f199552
category: bugfix
bugzilla: 107379 https://gitee.com/openeuler/kernel/issues/I4DDEL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6f1995523a0fac7dd4fc7d2f175604dd9f699338



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The function fib6_walk_continue() cannot return a positive value when
called from register_fib_notifier(), but ignoring causes static analyzer to
generate warnings in users of register_fib_notifier() that try to convert
returned error code to pointer with ERR_PTR(). Handle such case by
explicitly checking for positive error values and converting them to
-EINVAL in fib6_tables_dump().

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Huang Guobin <huangguobin4@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>