bridge: vlan: add global mcast_last_member_interval option

bridge: vlan: add global mcast_last_member_interval option

Add control and dump support for the global mcast_last_member_interval
option which controls the interval between queries to find remaining
members of a group after a leave message. To be consistent with the same
bridge-wide option the value is reported with USER_HZ granularity and
the same granularity is expected when setting it.
The default is 100 (1 second).
Syntax:
 $ bridge vlan global set dev bridge vid 1 mcast_last_member_interval 200

Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David Ahern <dsahern@kernel.org>