vxlan: vxlan_fdb_notify(): Make switchdev notification configurable

In a following patch, vxlan is extended to allow hardware FDB learning.
For FDB entries learned this way, switchdev notifications should not be
sent again, because the driver already knows about these entries.

To that end, add an argument vxlan_fdb_notify() to determine whether
the switchdev notifications should be sent. Propagate the argument to
all call sites transitively, eventually passing true in all root calls.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>