Merge branch 'mptcp-blackhole-only-if-1st-syn-retrans-w-o-mpc-is-accepted'

Matthieu Baerts says:

====================
mptcp: blackhole only if 1st SYN retrans w/o MPC is accepted

Here are two small fixes for issues introduced in v6.12.

- Patch 1: reset the mpc_drop mark for other SYN retransmits, to only
  consider an MPTCP blackhole when the first SYN retransmitted without
  the MPTCP options is accepted, as initially intended.

- Patch 2: also mention in the doc that the blackhole_timeout sysctl
  knob is per-netns, like all the others.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
====================

Link: https://patch.msgid.link/20250129-net-mptcp-blackhole-fix-v1-0-afe88e5a6d2c@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>