net/smc: Fix NULL pointer dereferencing in smc_vlan_by_tcpsk()

mainline inclusion
from mainline-v5.16-rc3
commit 587acad4
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9S242
CVE: CVE-2021-47559

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=587acad41f1bc48e16f42bb2aca63bf323380be8



--------------------------------

Coverity reports a possible NULL dereferencing problem:

in smc_vlan_by_tcpsk():
6. returned_null: netdev_lower_get_next returns NULL (checked 29 out of 30 times).
7. var_assigned: Assigning: ndev = NULL return value from netdev_lower_get_next.
1623                ndev = (struct net_device *)netdev_lower_get_next(ndev, &lower);
CID 1468509 (#1 of 1): Dereference null return value (NULL_RETURNS)
8. dereference: Dereferencing a pointer that might be NULL ndev when calling is_vlan_dev.
1624                if (is_vlan_dev(ndev)) {

Remove the manual implementation and use netdev_walk_all_lower_dev() to
iterate over the lower devices. While on it remove an obsolete function
parameter comment.

Fixes: cb9d43f6 ("net/smc: determine vlan_id of stacked net_device")
Suggested-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Conflicts:
        net/smc/smc_core.c
[The conflict occurs because the commit eff74233("net: core:
introduce struct netdev_nested_priv for nested interface
infrastructure") and bc36d2fc("net/smc: consolidate function
parameters") are not merged]
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>