ipv4: Fix error return code in fib_table_insert()

ipv4: Fix error return code in fib_table_insert()

[ Upstream commit 568fe84940ac0e4e0b2cd7751b8b4911f7b9c215 ]

In fib_table_insert(), if the alias was already inserted, but node not
exist, the error code should be set before return from error handling path.

Fixes: a6c76c17df02 ("ipv4: Notify route after insertion to the routing table")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Link: https://lore.kernel.org/r/20221120072838.2167047-1-william.xuanziyang@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>