mptcp: properly account fastopen data

mptcp: properly account fastopen data

Currently the socket level counter aggregating the received data
does not take in account the data received via fastopen.

Address the issue updating the counter as required.

Fixes: 38967f424b5b ("mptcp: track some aggregate data counters")
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20231023-send-net-next-20231023-2-v1-2-9dc60939d371@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>