dissolve libcommon-cs: move gsm48_* code to libmsc, drop sms_next_rp_msg_ref()

Move gsm48_* functions from common_cs.c to libmsc/gsm_04_08.c.

Drop sms_next_rp_msg_ref(), it is just a bunch of bloat around "next_rp_ref++".
Apply the "++" instead, in gsm_04_11.c.

libcommon-cs is now empty, to be removed in subsequent commit.

Change-Id: Ibc410803ce8e273b626124ab9fc934f04df3ae50
diff --git a/src/libmsc/gsm_04_11.c b/src/libmsc/gsm_04_11.c
index 45b56d2..f82aa6d 100644
--- a/src/libmsc/gsm_04_11.c
+++ b/src/libmsc/gsm_04_11.c
@@ -993,7 +993,7 @@
 	struct msgb *msg = gsm411_msgb_alloc();
 	struct gsm_trans *trans;
 	uint8_t *data, *rp_ud_len;
-	uint8_t msg_ref = sms_next_rp_msg_ref(&conn->next_rp_ref);
+	uint8_t msg_ref = conn->next_rp_ref++;
 	int transaction_id;
 	int rc;