mptcp: drop subflow contexts in mptcp_sched_data

The mptcp_subflow bpf_iter is added now, it's better to use the helper
bpf_for_each(mptcp_subflow) to traverse all subflows on the conn_list of
an MPTCP socket and then call kfunc to modify the fields of each subflow
in the WIP MPTCP BPF packet scheduler examples, instead of converting them
to a fixed array. With this helper, we can get rid of this subflow array
"contexts" and the size of it "subflows" in struct mptcp_sched_data.

Signed-off-by: Geliang Tang <[email protected]>

include/net/mptcp.h

@@ -104,8 +104,6 @@ struct mptcp_out_options {
 
 struct mptcp_sched_data {
 	bool	reinject;
-	u8	subflows;
-	struct mptcp_subflow_context *contexts[MPTCP_SUBFLOWS_MAX];
 };
 
 struct mptcp_sched_ops {