[lchan] RSL and RR need the multirate config, place it in the lchan

Both GSM 04.08 RR and GSM 08.58 RSL need the multirate config
in the channel modify. Place the config in the lchan, change
the gsm48 methods to not take the argument, change the RSL
implementation to make use of it with the right IE.

The other code should use the t(l)v_put routines as well but
were left untouched for now.
diff --git a/openbsc/src/abis_rsl.c b/openbsc/src/abis_rsl.c
index f6e0b87..0dee79b 100644
--- a/openbsc/src/abis_rsl.c
+++ b/openbsc/src/abis_rsl.c
@@ -648,6 +648,11 @@
 			msgb_tlv_put(msg, RSL_IE_ENCR_INFO, rc, encr_info);
 	}
 
+	if (lchan->tch_mode == GSM48_CMODE_SPEECH_AMR) {
+		msgb_tlv_put(msg, RSL_IE_MR_CONFIG, sizeof(lchan->mr_conf),
+			     (u_int8_t *) &lchan->mr_conf);
+	}
+
 	msg->trx = lchan->ts->trx;
 
 	return abis_rsl_sendmsg(msg);