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>

net/sctp/sm_make_chunk.c

@@ -1782,7 +1782,7 @@ no_hmac:
 	else
 		kt = ktime_get();
 
-	if (!asoc && ktime_compare(bear_cookie->expiration, kt) < 0) {
+	if (!asoc && ktime_before(bear_cookie->expiration, kt)) {
 		/*
 		 * Section 3.3.10.3 Stale Cookie Error (3)
 		 *