lcls: do not LCLS call legs with different codecs

It is theoretically possible to LCLS two legs that use different
codecs. However, this requires transcoding capabilities on the
local MGW. If the local MGW lacks transcoding features such a
local circuit should be avoided. Enabeling LCLS under such
coditions should be optional (VTY)

- Add check to avoid LCLS on different codec/rate
- Add VTY-Option to optionally override the check
  (MGW is able to transcode)

Change-Id: I157549129a40c64364dc126f67195759e5f1d60f
Related: OS#1602
diff --git a/include/osmocom/bsc/bsc_msc_data.h b/include/osmocom/bsc/bsc_msc_data.h
index 79d2eca..7ec3442 100644
--- a/include/osmocom/bsc/bsc_msc_data.h
+++ b/include/osmocom/bsc/bsc_msc_data.h
@@ -87,6 +87,7 @@
 	struct gsm_audio_support **audio_support;
 	int audio_length;
 	enum bsc_lcls_mode lcls_mode;
+	bool lcls_codec_mismatch_allow;
 
 	/* ussd welcome text */
 	char *ussd_welcome_txt;