net: amt: convert to use secs_to_jiffies

Since secs_to_jiffies()(commit:b35108a5) has been introduced, we can
use it to avoid scaling the time to msec.

Signed-off-by: Yuesong Li <liyuesong@vivo.com>
Reviewed-by: Joe Damato <joe@dama.to>
Reviewed-by: Taehee Yoo <ap420073@gmail.com>
Link: https://patch.msgid.link/20250613102014.3070898-1-liyuesong@vivo.com


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