bsc: lchan_select: Avoid returning a TCH/H lchan when TCH/F is requested

If BTS is configured to have only TCH/F_PDCH and TCH/H and a call is
resolved to require TCH/F, don't return the TCH/H which have no use, but
instead let it allocate the TCH/F_PDCH.

20181128185013783 DRLL <0000> lchan_select.c:159 (bts=0) lchan_select_by_type(TCH_F)
20181128185013783 DRLL <0000> lchan_select.c:71 looking for lchan TCH/F: (bts=0,trx=0,ts=0,pchan=CCCH+SDCCH4,state=IN_USE) is != TCH/F
20181128185013783 DRLL <0000> lchan_select.c:71 looking for lchan TCH/F: (bts=0,trx=0,ts=1,pchan=SDCCH8,state=UNUSED) is != TCH/F
20181128185013783 DRLL <0000> lchan_select.c:71 looking for lchan TCH/F: (bts=0,trx=0,ts=2,pchan=TCH/H,state=UNUSED) is != TCH/F
20181128185013783 DRLL <0000> lchan_select.c:71 looking for lchan TCH/F: (bts=0,trx=0,ts=3,pchan=TCH/H,state=UNUSED) is != TCH/F
20181128185013783 DRLL <0000> lchan_select.c:71 looking for lchan TCH/F: (bts=0,trx=0,ts=4,pchan=TCH/H,state=UNUSED) is != TCH/F
20181128185013783 DRLL <0000> lchan_select.c:71 looking for lchan TCH/F: (bts=0,trx=0,ts=5,pchan=TCH/H,state=UNUSED) is != TCH/F
20181128185013783 DRLL <0000> lchan_select.c:71 looking for lchan TCH/F: (bts=0,trx=0,ts=6,pchan_on_init=TCH/F_PDCH,pchan=PDCH,state=PDCH) is != TCH/F
20181128185013784 DRLL <0000> lchan_select.c:71 looking for lchan TCH/F: (bts=0,trx=0,ts=7,pchan_on_init=TCH/F_PDCH,pchan=PDCH,state=PDCH) is != TCH/F
20181128185013784 DRLL <0000> lchan_select.c:71 looking for lchan TCH/H: (bts=0,trx=0,ts=0,pchan=CCCH+SDCCH4,state=IN_USE) is != TCH/H
20181128185013784 DRLL <0000> lchan_select.c:71 looking for lchan TCH/H: (bts=0,trx=0,ts=1,pchan=SDCCH8,state=UNUSED) is != TCH/H
20181128185013784 DRLL <0000> lchan_select.c:86 looking for lchan TCH/H: (bts=0,trx=0,ts=2,pchan=TCH/H,state=UNUSED) ss=0 is available
20181128185013784 DCHAN <0010> lchan_select.c:253 lchan(0-0-2-TCH_H-0)[0x6120000066a0]{UNUSED}: (type=TCH_H) Selected

Change-Id: I9a73beb0432fab16d5430e5b40d470694e09b189
diff --git a/src/osmo-bsc/lchan_select.c b/src/osmo-bsc/lchan_select.c
index 742c7de..f70ad4a 100644
--- a/src/osmo-bsc/lchan_select.c
+++ b/src/osmo-bsc/lchan_select.c
@@ -182,13 +182,7 @@
 		break;
 	case GSM_LCHAN_TCH_F:
 		lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F);
-		/* If we don't have TCH/F available, fall-back to TCH/H */
-		if (!lchan) {
-			lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_H);
-			if (lchan)
-				type = GSM_LCHAN_TCH_H;
-		}
-		/* If we don't have TCH/H either, try dynamic TCH/F_PDCH */
+		/* If we don't have TCH/F available, try dynamic TCH/F_PDCH */
 		if (!lchan) {
 			lchan = _lc_dyn_find_bts(bts, GSM_PCHAN_TCH_F_PDCH,
 						 GSM_PCHAN_TCH_F);
@@ -206,14 +200,6 @@
 			if (lchan)
 				type = GSM_LCHAN_TCH_F;
 		}
-		/* ...and as TCH/H. */
-		if (!lchan) {
-			lchan = _lc_dyn_find_bts(bts,
-						 GSM_PCHAN_TCH_F_TCH_H_PDCH,
-						 GSM_PCHAN_TCH_H);
-			if (lchan)
-				type = GSM_LCHAN_TCH_H;
-		}
 		break;
 	case GSM_LCHAN_TCH_H:
 		lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_H);
@@ -257,4 +243,3 @@
 
 	return lchan;
 }
-