trxcon/scheduler: fix subst_frame_loss(): do not compensate too much

It's not something that we should be trying to fix, if the whole
TDMA multi-frame is lost.  For some yet unknown reason, sometimes
the difference between the last processed TDMA frame number and
the current one is so huge, so trxcon eats a lot of CPU trying
to compensate nearly the whole TDMA hyper-frame:

  sched_trx.c:640 Too many (>104) contiguous TDMA frames elapsed (2715647)
                  since the last processed fn=633 (current fn=632)

Let's just print a warning and do not compensate more than one
TDMA multi-frame period corresponding to the current layout.

Change-Id: I56251d0d2f6fa19195ff105d3bdfbc22df6db8cd

src/host/trxcon/sched_trx.c

@@ -640,6 +640,7 @@ static int subst_frame_loss(struct trx_lchan_state *lchan,
 		LOGP(DSCHD, LOGL_NOTICE, "Too many (>%u) contiguous TDMA frames elapsed (%u) "
 					 "since the last processed fn=%u (current %u)\n",
 					 mf->period, elapsed, lchan->tdma.last_proc, fn);
+		return -EIO;
 	} else if (elapsed == 0) {
 		LOGP(DSCHD, LOGL_ERROR, "No TDMA frames elapsed since the last processed "
 					"fn=%u, must be a bug?\n", lchan->tdma.last_proc);