Changing MTU on a link currently causes 3 messages to be sent to userspace:
[LINK]11: dummy1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1490 qdisc noqueue state UNKNOWN group default
    link/ether f2:52:5c:6d:21:f3 brd ff:ff:ff:ff:ff:ff
[LINK]11: dummy1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default
    link/ether f2:52:5c:6d:21:f3 brd ff:ff:ff:ff:ff:ff
[LINK]11: dummy1: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default
    link/ether f2:52:5c:6d:21:f3 brd ff:ff:ff:ff:ff:ff
Remove the messages sent for PRE_CHANGE_MTU and CHANGE_MTU netdev events.
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 
        switch (event) {
        case NETDEV_REBOOT:
-       case NETDEV_CHANGEMTU:
        case NETDEV_CHANGEADDR:
        case NETDEV_CHANGENAME:
        case NETDEV_FEAT_CHANGE:
        case NETDEV_NOTIFY_PEERS:
        case NETDEV_CHANGEUPPER:
        case NETDEV_RESEND_IGMP:
-       case NETDEV_PRECHANGEMTU:
        case NETDEV_CHANGEINFODATA:
        case NETDEV_PRECHANGEUPPER:
        case NETDEV_CHANGELOWERSTATE: