treewide: Address cert-err33-c clang-tidy warnings for clock and timer functions

For clock_gettime(), we shouldn't ignore errors if they happen at
initialisation phase, because something is seriously wrong and it's
not helpful if we proceed as if nothing happened.

As we're up and running, though, it's probably better to report the
error and use a stale value than to terminate altogether. Make sure
we use a zero value if we don't have a stale one somewhere.

For timerfd_gettime() and timerfd_settime() failures, just report an
error, there isn't much else we can do.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

tcp.c

@@ -549,7 +549,8 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn *conn)
 		 (unsigned long long)it.it_value.tv_sec,
 		 (unsigned long long)it.it_value.tv_nsec / 1000 / 1000);
 
-	timerfd_settime(conn->timer, 0, &it, NULL);
+	if (timerfd_settime(conn->timer, 0, &it, NULL))
+		flow_err(conn, "failed to set timer: %s", strerror(errno));
 }
 
 /**
@@ -2235,7 +2236,9 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref)
 	 * timer is currently armed, this event came from a previous setting,
 	 * and we just set the timer to a new point in the future: discard it.
 	 */
-	timerfd_gettime(conn->timer, &check_armed);
+	if (timerfd_gettime(conn->timer, &check_armed))
+		flow_err(conn, "failed to read timer: %s", strerror(errno));
+
 	if (check_armed.it_value.tv_sec || check_armed.it_value.tv_nsec)
 		return;
 
@@ -2273,7 +2276,10 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref)
 		 * case. This avoids having to preemptively reset the timer on
 		 * ~ACK_TO_TAP_DUE or ~ACK_FROM_TAP_DUE.
 		 */
-		timerfd_settime(conn->timer, 0, &new, &old);
+		if (timerfd_settime(conn->timer, 0, &new, &old))
+			flow_err(conn, "failed to set timer: %s",
+				 strerror(errno));
+
 		if (old.it_value.tv_sec == ACT_TIMEOUT) {
 			flow_dbg(conn, "activity timeout");
 			tcp_rst(c, conn);