mptcp: Use MPTCP-level flag for sending DATA_FIN

Since DATA_FIN information is the same for every subflow, store it only
in the mptcp_sock.

Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
3 files changed