net: ti: icssg-prueth: Fix link-local addresses being forwarded out of slave ports

Link-local multicast addresses (01:80:c2:00:00:0x) must only be
delivered to the host port (P0) and must not be forwarded out of
the physical slave ports. icssg_fdb_add_del() was programming these
addresses with P1/P2 membership bits set, causing the firmware to
forward them out of slave ports.

Clear P1/P2 membership and set only P0 membership when
is_link_local_ether_addr() returns true.

Fixes: 487f7323f39a ("net: ti: icssg-prueth: Add helper functions to configure FDB")
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>