tcp: add TCP_MINTTL drop reason

In the unlikely case incoming packets are dropped because
of IP_MINTTL / IPV6_MINHOPCOUNT constraints...

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230201174345.2708943-1-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>