net: ti: icssg-prueth: Fix race condition for VLAN table access

The VLAN table is a shared memory between the two ports/slices
in a ICSSG cluster and this may lead to race condition when the
common code paths for both ports are executed in different CPUs.

Fix the race condition access by locking the shared memory access

Fixes: 487f7323 ("net: ti: icssg-prueth: Add helper functions to configure FDB")
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>