osmux: Don't process regular osmux frames if disabled by cfg

Prior to this commit, the check was only done on legacy dummy frames.

Port from openbsc a42d4584fd01c9cd1021fab609bdaaafe859c13a.
Change-Id: I5b6606d72a9f5ae593a8e3ab5fbbe7e1e5a0ae11
diff --git a/src/libosmo-mgcp/mgcp_osmux.c b/src/libosmo-mgcp/mgcp_osmux.c
index 2e58c55..2e6307e 100644
--- a/src/libosmo-mgcp/mgcp_osmux.c
+++ b/src/libosmo-mgcp/mgcp_osmux.c
@@ -331,6 +331,12 @@
 	if (!msg)
 		return -1;
 
+	if (!cfg->osmux) {
+		LOGP(DLMGCP, LOGL_ERROR,
+		     "bsc-nat wants to use Osmux but bsc did not request it\n");
+		goto out;
+	}
+
 	/* not any further processing dummy messages */
 	if (msg->data[0] == MGCP_DUMMY_LOAD)
 		goto out;
@@ -382,12 +388,6 @@
 	LOGP(DLMGCP, LOGL_DEBUG, "Received Osmux dummy load from %s\n",
 	     inet_ntoa(addr->sin_addr));
 
-	if (!cfg->osmux) {
-		LOGP(DLMGCP, LOGL_ERROR,
-		     "bsc wants to use Osmux but bsc-nat did not request it\n");
-		goto out;
-	}
-
 	/* extract the osmux CID from the dummy message */
 	memcpy(&osmux_cid, &msg->data[1], sizeof(osmux_cid));
 
@@ -433,6 +433,12 @@
 	if (!msg)
 		return -1;
 
+	if (!cfg->osmux) {
+		LOGP(DLMGCP, LOGL_ERROR,
+		     "bsc wants to use Osmux but bsc-nat did not request it\n");
+		goto out;
+	}
+
 	/* not any further processing dummy messages */
 	if (msg->data[0] == MGCP_DUMMY_LOAD)
 		return osmux_handle_dummy(cfg, &addr, msg);