net: use batched device unregister in veth and macvlan
veth devices dont use the batched device unregisters yet.
Since veth are a pair of devices, it makes sense to use a batch of two
unregisters, this roughly divides dismantle time by two.
Fix this by changing dellink() callers to always provide a non NULL
head. (Idea from Michał Mirosław)
This patch also handles macvlan case : We now dismantle all macvlans on
top of a lower dev at once.
Reported-by: Alex Bligh <alex@alex.org.uk> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Cc: Michał Mirosław <mirqus@gmail.com> Cc: Jesse Gross <jesse@nicira.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ben Greear <greearb@candelatech.com> Signed-off-by: David S. Miller <davem@davemloft.net>