Revert "net: dsa: mv88e6xxx: flush switchdev FDB workqueue before removing VLAN"

This reverts commit 2566a89b which is
commit a2614140dc0f467a83aa3bb4b6ee2d6480a76202 upstream.

The above change depends on upstream commit 0faf890f ("net: dsa:
drop rtnl_lock from dsa_slave_switchdev_event_work"), which is not
present in linux-5.15.y. Without that change, waiting for the switchdev
workqueue causes deadlocks on the rtnl_mutex.

Backporting the dependency commit isn't trivial/desirable, since it
requires that the following dependencies of the dependency are also
backported:

df405910 net: dsa: sja1105: wait for dynamic config command completion on writes too
eb016afd net: dsa: sja1105: serialize access to the dynamic config interface
2468346c net: mscc: ocelot: serialize access to the MAC table
f7eb4a1c net: dsa: b53: serialize access to the ARL table
cf231b43 net: dsa: lantiq_gswip: serialize access to the PCE registers
338a3a47 net: dsa: introduce locking for the address lists on CPU and DSA ports

and then this bugfix on top:

8940e6b669ca ("net: dsa: avoid call to __dev_set_promiscuity() while rtnl_mutex isn't held")

Reported-by: Daniel Suchy <danny@danysek.cz>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>