net: reinstate rtnl in call_netdevice_notifiers()

net: reinstate rtnl in call_netdevice_notifiers()

Eric Biederman pointed out that not holding RTNL while calling
call_netdevice_notifiers() was racy.

This patch is a direct transcription his feedback
against commit 0115e8e30d6fc (net: remove delay at device dismantle)

Thanks Eric !

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Tom Herbert <[email protected]>
Cc: Mahesh Bandewar <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Gao feng <[email protected]>
Acked-by: "Eric W. Biederman" <[email protected]>
Signed-off-by: David S. Miller <[email protected]>