dsa: mv88e6xxx: Include tagger overhead when setting MTU for DSA and CPU ports

stable inclusion
from stable-5.10.71
commit c20a0ad7b6a054d77c3f20660befe77eaae3f24d
bugzilla: 182981 https://gitee.com/openeuler/kernel/issues/I4I3KD

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c20a0ad7b6a054d77c3f20660befe77eaae3f24d



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

[ Upstream commit b9c587fe ]

Same members of the Marvell Ethernet switches impose MTU restrictions
on ports used for connecting to the CPU or another switch for DSA. If
the MTU is set too low, tagged frames will be discarded. Ensure the
worst case tagger overhead is included in setting the MTU for DSA and
CPU ports.

Fixes: 1baf0fac ("net: dsa: mv88e6xxx: Use chip-wide max frame size for MTU")
Reported by: 曹煜 <cao88yu@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>