[SCTP]: Fix sctp_cookie alignment in the packet.

On 64 bit architectures, sctp_cookie sent as part of INIT-ACK is not
aligned on a 64 bit boundry and thus causes unaligned access exceptions.

The layout of the cookie prameter is this:
|<----- Parameter Header --------------------|<--- Cookie DATA --------
-----------------------------------------------------------------------
| param type (16 bits) | param len (16 bits) | sig [32 bytes] | cookie..
-----------------------------------------------------------------------

The cookie data portion contains 64 bit values on 64 bit architechtures
(timeval) that fall on a 32 bit alignment boundry when used as part of
the on-wire format, but align correctly when used in internal
structures.  This patch explicitely pads the on-wire format so that
it is properly aligned.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>

include/net/sctp/structs.h

@@ -405,8 +405,9 @@ struct sctp_cookie {
 /* The format of our cookie that we send to our peer. */
 struct sctp_signed_cookie {
 	__u8 signature[SCTP_SECRET_SIZE];
+	__u32 __pad;		/* force sctp_cookie alignment to 64 bits */
 	struct sctp_cookie c;
-};
+} __attribute__((packed));
 
 /* This is another convenience type to allocate memory for address
  * params for the maximum size and pass such structures around