ocelot: Dont allocate another multicast list, use __dev_mc_sync

Doing kmalloc in atomic context is always an issue,
more so for a list that can grow significantly.
Turns out that the driver only uses the duplicated
list of multicast mac addresses to keep track of
what addresses to delete from h/w before committing
the new list from kernel to h/w back again via set_rx_mode,
every time this list gets updated by the kernel.
Given that the h/w knows how to add and delete mac addresses
based on the mac address value alone, __dev_mc_sync should be
the much better choice of kernel API for these operations
avoiding the considerable overhead of maintaining a duplicated
list in the driver.

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Tested-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>