sctp: not copying duplicate addrs to the assoc's bind address list

sctp.local_addr_list is a global address list that is supposed to include
all the local addresses. sctp updates this list according to NETDEV_UP/
NETDEV_DOWN notifications.

However, if multiple NICs have the same address, the global list would
have duplicate addresses. Even if for one NIC, promote secondaries in
__inet_del_ifa can also lead to accumulating duplicate addresses.

When sctp binds address 'ANY' and creates a connection, it copies all
the addresses from global list into asoc's bind addr list, which makes
sctp pack the duplicate addresses into INIT/INIT_ACK packets.

This patch is to filter the duplicate addresses when copying the addrs
from global list in sctp_copy_local_addr_list and unpacking addr_param
from cookie in sctp_raw_to_bind_addrs to asoc's bind addr list.

Note that we can't filter the duplicate addrs when global address list
gets updated, As NETDEV_DOWN event may remove an addr that still exists
in another NIC.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>