Modify PI servo to set frequency when jumping.

Similarly to the servo in phc2sys, when clock is stepped, set
immediately also its frequency. This significantly improves the initial
convergence with large frequency offsets.

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>

clock.c

@@ -867,6 +867,7 @@ enum servo_state clock_synchronize(struct clock *c,
 	case SERVO_UNLOCKED:
 		break;
 	case SERVO_JUMP:
+		clock_ppb(c->clkid, -adj);
 		clock_step(c->clkid, -c->master_offset);
 		c->t1 = tmv_zero();
 		c->t2 = tmv_zero();

pi.c

@@ -87,6 +87,7 @@ static double pi_sample(struct servo *servo,
 		break;
 	case 3:
 		*state = SERVO_JUMP;
+		ppb = s->drift;
 		s->count = 4;
 		break;
 	case 4: