[NET]: Messed multicast lists after dev_mc_sync/unsync

Commit a0a400d7 ("[NET]: dev_mcast:
add multicast list synchronization helpers") from you introduced a new
field "da_synced" to struct dev_addr_list that is not properly
initialized to 0. So when any of the current users (8021q, macvlan,
mac80211) calls dev_mc_sync/unsync they mess the address list for both
devices.

The attached patch fixed it for me and avoid future problems.
Signed-off-by: NJorge Boncompte [DTI2] <jorge@dti2.net>
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2900,7 +2900,7 @@ int __dev_addr_add(struct dev_addr_list **list, int *count,
 		}
 	}
 
-	da = kmalloc(sizeof(*da), GFP_ATOMIC);
+	da = kzalloc(sizeof(*da), GFP_ATOMIC);
 	if (da == NULL)
 		return -ENOMEM;
 	memcpy(da->da_addr, addr, alen);