net: bridge: vlan: notify on vlan add/delete/change flags

Now that we can notify, send a notification on add/del or change of flags.
Notifications are also compressed when possible to reduce their number
and relieve user-space of extra processing, due to that we have to
manually notify after each add/del in order to avoid double
notifications. We try hard to notify only about the vlans which actually
changed, thus a single command can result in multiple notifications
about disjoint ranges if there were vlans which didn't change inside.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>