xfrm: Make xfrm_state timer monotonic

xfrm_state timer should be independent of system clock change,
so switch to CLOCK_BOOTTIME base which is not only monotonic but
also counting suspend time.

Thus issue reported in commit: 9e0d57fd
("xfrm: SAD entries do not expire correctly after suspend-resume")
could ALSO be avoided.

v2: Use CLOCK_BOOTTIME to count suspend time, but still monotonic.
Signed-off-by: Fan Du <fan.du@windriver.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_state.c

@@ -499,7 +499,8 @@ struct xfrm_state *xfrm_state_alloc(struct net *net)
 		INIT_HLIST_NODE(&x->bydst);
 		INIT_HLIST_NODE(&x->bysrc);
 		INIT_HLIST_NODE(&x->byspi);
-		tasklet_hrtimer_init(&x->mtimer, xfrm_timer_handler, CLOCK_REALTIME, HRTIMER_MODE_ABS);
+		tasklet_hrtimer_init(&x->mtimer, xfrm_timer_handler,
+					CLOCK_BOOTTIME, HRTIMER_MODE_ABS);
 		setup_timer(&x->rtimer, xfrm_replay_timer_handler,
 				(unsigned long)x);
 		x->curlft.add_time = get_seconds();