mptcp: fix possible integer overflow in mptcp_reset_tout_timer

commit b169e76e upstream.

In 'mptcp_reset_tout_timer', promote 'probe_timestamp' to unsigned long
to avoid possible integer overflow. Compile tested only.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Dmitry Kandybka <d.kandybka@gmail.com>
Link: https://patch.msgid.link/20241107103657.1560536-1-d.kandybka@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflict in this version because commit d866ae9a ("mptcp: add a
  new sysctl for make after break timeout") is not in this version, and
  replaced TCP_TIMEWAIT_LEN in the expression. The fix can still be
  applied the same way: by forcing a cast to unsigned long for the first
  item. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>