nat: Look at the assignment command and remember on which timeslot the data is

This information will be needed when we are trying to forward
MGCP connections to and from the BSC through the IPA protocol.
diff --git a/openbsc/tests/bsc-nat/bsc_data.c b/openbsc/tests/bsc-nat/bsc_data.c
index b73aff1..ca170e2 100644
--- a/openbsc/tests/bsc-nat/bsc_data.c
+++ b/openbsc/tests/bsc-nat/bsc_data.c
@@ -80,3 +80,10 @@
 0x10, 0x52, 0x08, 0x08, 0x29, 0x47, 0x10, 0x02,
 0x01, 0x50, 0x02, 0x30, 0x1a, 0x03, 0x05, 0x20,
 0x15 };
+
+/* an assignment command */
+static const u_int8_t ass_cmd[] = {
+0x00, 0x12, 0xfd, 0x06,
+0x00, 0x00, 0x49, 0x00, 0x01, 0x0b, 0x00, 0x09,
+0x01, 0x0b, 0x03, 0x01, 0x0a, 0x11, 0x01, 0x00,
+0x15 };