sctp: check addr_size with sa_family_t size in __sctp_setsockopt_connectx

Now __sctp_connect() is called by __sctp_setsockopt_connectx() and
sctp_inet_connect(), the latter has done addr_size check with size
of sa_family_t.

In the next patch to clean up __sctp_connect(), we will remove
addr_size check with size of sa_family_t from __sctp_connect()
for the 1st address.

So before doing that, __sctp_setsockopt_connectx() should do
this check first, as sctp_inet_connect() does.

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