The current implementation of 32 bit DSN expansion is buggy.
After the previous patch, we can simply reuse the newly
introduced helper to do the expansion safely.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/120
Fixes: 648ef4b8 ("mptcp: Implement MPTCP receive path")
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>