sctp: use time_before or time_after for comparing jiffies

The functions time_before or time_after are more robust
for comparing jiffies against other values.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>