dn_route: replace "jiffies-now>0" with "jiffies!=now"

Use "jiffies != now" to replace "jiffies - now > 0" to make
code more readable. We want to put a limit on how long the
loop can run for before rescheduling.

Signed-off-by: Yu Zhe <yuzhe@nfschina.com>
Link: https://lore.kernel.org/r/20220729061712.22666-1-yuzhe@nfschina.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>