amr: Instead of putting ms/bts into the same struct.. use it twice

This way a lot of if/else can just be killed by the caller deciding
which of the two instances to use.

I have copied both branches to new files, replace bts for ms in one
of them and ran diff on it. There is no difference.
diff --git a/openbsc/src/libbsc/bsc_api.c b/openbsc/src/libbsc/bsc_api.c
index 78e7c87..e157eb9 100644
--- a/openbsc/src/libbsc/bsc_api.c
+++ b/openbsc/src/libbsc/bsc_api.c
@@ -178,8 +178,8 @@
 		mr_conf->icmi = 1;
 		mr_conf->m5_90 = 1;
 	}
-	gsm48_multirate_config(lchan->mr_ms_lv, mr, 1);
-	gsm48_multirate_config(lchan->mr_bts_lv, mr, 0);
+	gsm48_multirate_config(lchan->mr_ms_lv, mr, mr->ms_mode);
+	gsm48_multirate_config(lchan->mr_bts_lv, mr, mr->bts_mode);
 }
 
 /*