bridge: export multicast database via netlink

V5: fix two bugs pointed out by Thomas
    remove seq check for now, mark it as TODO

V4: remove some useless #include
    some coding style fix

V3: drop debugging printk's
    update selinux perm table as well

V2: drop patch 1/2, export ifindex directly
    Redesign netlink attributes
    Improve netlink seq check
    Handle IPv6 addr as well

This patch exports bridge multicast database via netlink
message type RTM_GETMDB. Similar to fdb, but currently bridge-specific.
We may need to support modify multicast database too (RTM_{ADD,DEL}MDB).

(Thanks to Thomas for patient reviews)

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Cong Wang <amwang@redhat.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/security/selinux/nlmsgtab.c b/security/selinux/nlmsgtab.c
index d309e7f..163aaa7 100644
--- a/security/selinux/nlmsgtab.c
+++ b/security/selinux/nlmsgtab.c
@@ -67,6 +67,7 @@
 	{ RTM_GETADDRLABEL,	NETLINK_ROUTE_SOCKET__NLMSG_READ  },
 	{ RTM_GETDCB,		NETLINK_ROUTE_SOCKET__NLMSG_READ  },
 	{ RTM_SETDCB,		NETLINK_ROUTE_SOCKET__NLMSG_WRITE },
+	{ RTM_GETMDB,		NETLINK_ROUTE_SOCKET__NLMSG_READ  },
 };
 
 static struct nlmsg_perm nlmsg_tcpdiag_perms[] =