sctp: fix overrun in sctp_diag_dump_one()

The function sctp_diag_dump_one() currently performs a memcpy()
of 64 bytes from a 16 byte field into another 16 byte field. Fix
by using correct size, use sizeof to obtain correct size instead
of using a hard-coded constant.

Fixes: 8f840e47

 ("sctp: add the sctp_diag.c file")
Signed-off-by: Lance Richardson <lrichard@redhat.com>
Reviewed-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>