net: mscc: ocelot: classify L2 mdb entries as LOCKED

ocelot.h says:

/* MAC table entry types.
 * ENTRYTYPE_NORMAL is subject to aging.
 * ENTRYTYPE_LOCKED is not subject to aging.
 * ENTRYTYPE_MACv4 is not subject to aging. For IPv4 multicast.
 * ENTRYTYPE_MACv6 is not subject to aging. For IPv6 multicast.
 */

We don't want the permanent entries added with 'bridge mdb' to be
subject to aging.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>