net/packet: convert po->auxdata to an atomic flag

stable inclusion
from stable-v4.19.283
commit e70e38104e5ecd6717f46f054592ba2683c5c7c3
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7BZ5U


CVE: NA

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

[ Upstream commit fd53c297 ]

po->auxdata can be read while another thread
is changing its value, potentially raising KCSAN splat.

Convert it to PACKET_SOCK_AUXDATA flag.

Fixes: 8dc41944 ("[PACKET]: Add optional checksum computation for recvmsg")
Signed-off-by: Eric Dumazet <edumazet@google.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>