trxcon/scheduler: fix n_errors for BFI triggered by FACCH

These BFI (Bad Frame Indications) substitute speech frames stolen
by FACCH/F or FACCH/H frames, so there can be no bit errors in
something that was not even transmitted over the air interface.

Change-Id: Icdb6209f75ead6581e3c18aeee0da9831aaa272a

src/host/trxcon/sched_lchan_tchf.c

@@ -155,7 +155,9 @@ bfi:
 			.toa256 = 0,
 			.rssi = -110,
 		};
-		n_errors = 116 * 4;
+
+		/* No bursts => no errors */
+		n_errors = 0;
 	}
 
 	/* BFI is not applicable in signalling mode */

src/host/trxcon/sched_lchan_tchh.c

@@ -349,7 +349,9 @@ bfi:
 			.toa256 = 0,
 			.rssi = -110,
 		};
-		n_errors = 116 * 2;
+
+		/* No bursts => no errors */
+		n_errors = 0;
 	}
 
 	/* Calculate TDMA frame number of the first burst */