mptcp: schedule rtx timer only after pushing data

mptcp: schedule rtx timer only after pushing data

The MPTCP protocol usually schedule the retransmission timer only
when there is some chances for such retransmissions to happen.

With a notable exception: __mptcp_push_pending() currently schedule
such timer unconditionally, potentially leading to unnecessary rtx
timer expiration.

The issue is present since the blamed commit below but become easily
reproducible after commit 27b0e701d387 ("mptcp: drop bogus optimization
in __mptcp_check_push()")

Fixes: 33d41c9cd74c ("mptcp: more accurate timeout")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251205-net-mptcp-misc-fixes-6-19-rc1-v1-3-9e4781a6c1b8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>