[SCTP] Fix SCTP socket options to work with 32-bit apps on 64-bit kernels.

Adds alignment attribute to a few structures used with SCTP socket
options so that the sizes and offsets remain the same when built using
either 32 or 64 bit tools.

Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>