Fix length issue of sctp_primary_addr.pkt on Linux

Before fix:
   sctp_primary_addr.pkt:13: runtime error in setsockopt call: Expected result 0 but got -1 with errno 22 (Invalid argument)

After fix:
   test passed both on Linux x86_64 and ppc64le

Signed-off-by: Jianwen Ji <jijianwen@gmail.com>