sctp: lack the check for ports in sctp_v6_cmp_addr

As the member .cmp_addr of sctp_af_inet6, sctp_v6_cmp_addr should also check
the port of addresses, just like sctp_v4_cmp_addr, cause it's invoked by
sctp_cmp_addr_exact().

Now sctp_v6_cmp_addr just check the port when two addresses have different
family, and lack the port check for two ipv6 addresses. that will make
sctp_hash_cmp() cannot work well.

so fix it by adding ports comparison in sctp_v6_cmp_addr().

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>