When parsing MPC+data packets we set the dss field, so
we must also initialize the data_fin, or we can find stray
value there.
Fixes: 9a19371bf029 ("mptcp: fix data_fin handing in RX path") Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>