[nat] Separate exit2/exit3 as this can not be shared...

We have tried to send a refuse for arbitary things and ended
up with a segfault... separate the exi2 and exit3 label to have
separate exits and cleanups.
diff --git a/openbsc/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index daed239..f21fe02 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -670,6 +670,11 @@
 		goto exit2;
 	}
 
+exit2:
+	talloc_free(parsed);
+	msgb_free(msg);
+	return -1;
+
 exit3:
 	/* send a SCCP Connection Refused */
 	refuse = sccp_create_refuse(parsed->src_local_ref, SCCP_REFUSAL_SCCP_FAILURE);
@@ -677,7 +682,7 @@
 		bsc_send_data(bsc, refuse->l2h, msgb_l2len(refuse), IPAC_PROTO_SCCP);
 		msgb_free(refuse);
 	}
-exit2:
+
 	talloc_free(parsed);
 	msgb_free(msg);
 	return -1;