ktime: add ktime_after and ktime_before helper

Add two minimal helper functions analogous to time_before() and
time_after() that will later on both be needed by SCTP code.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/linux/ktime.h
Simple merge

diff --cc net/sctp/sm_make_chunk.c
Simple merge