net/packet: fix packet_sock xmit return value checking

stable inclusion
from stable-4.19.240
commit 9be70070b00c9f3a55d89a98f08264725cf45981
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5A6BA


CVE: NA

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

[ Upstream commit 29e8e659 ]

packet_sock xmit could be dev_queue_xmit, which also returns negative
errors. So only checking positive errors is not enough, or userspace
sendmsg may return success while packet is not send out.

Move the net_xmit_errno() assignment in the braces as checkpatch.pl said
do not use assignment in if condition.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>