net: bridge: switchdev: fix shim definition for br_switchdev_mdb_notify

net: bridge: switchdev: fix shim definition for br_switchdev_mdb_notify

br_switchdev_mdb_notify() is conditionally compiled only when
CONFIG_NET_SWITCHDEV=y and CONFIG_BRIDGE_IGMP_SNOOPING=y. It is called
from br_mdb.c, which is conditionally compiled only when
CONFIG_BRIDGE_IGMP_SNOOPING=y.

The shim definition of br_switchdev_mdb_notify() is therefore needed for
the case where CONFIG_NET_SWITCHDEV=n, however we mistakenly put it
there for the case where CONFIG_BRIDGE_IGMP_SNOOPING=n. This results in
build failures when CONFIG_BRIDGE_IGMP_SNOOPING=y and
CONFIG_NET_SWITCHDEV=n.

To fix this, put the shim definition right next to
br_switchdev_fdb_notify(), which is properly guarded by NET_SWITCHDEV=n.
Since this is called only from br_mdb.c, we need not take any extra
safety precautions, when NET_SWITCHDEV=n and BRIDGE_IGMP_SNOOPING=n,
this shim definition will be absent but nobody will be needing it.

Fixes: 9776457c784f ("net: bridge: mdb: move all switchdev logic to br_switchdev.c")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20211029223606.3450523-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>